[x3aniac]

Link: https://streamable.com/vq4bwq

Hello,

*FYI trunk left side doesn't have sound insulation at the moment, rear shocks and springs have been changed a month ago (alignment is not done yet, the car feels quite floaty and not as agile as before, that might be something to keep in mind).*

I've got an X3 F25 and there's a strange sound coming from the left rear of the car when accelerating and also deaccelerating. It has been there for a good half a year. Recently had to drive at higher speeds and noticed that it didn't quiet down, half a year ago it occurred somewhere from 80kmh to 90kmh and then seemed to quiet down. First we thought that maybe it was the wheel bearing, but after taking off the wheels, both of them on each side looked the same, gave it some scuffing up, and called it a day. The rear rotors and brake pads aren't in the best condition, couple of people have mentioned it since 2022 August (maybe this has to do with something). Yesterday drove it fast on the highway and had to slam on the brakes because a car jumped in front, now under braking, I can feel the knocking, looks like I've warped the discs/rotors. What could be the problem?

Also, I'm attaching a video with a link that a person in the front passenger seat had recorded. I can clearly hear the sound on my phone, but while with my earphones it's quite hard unless I manage to find the perfect volume spot. The video features both sounds while accelerating and also deaccelerating around 120-150kmh.

Hope someone would be able to help. Happy late Christmas and wish you a good upcoming New Year.

[Opie55]

Right near the end of that clip it sounds like the same sound I have. Does it kind of sound like you are being followed by a small airplane?

[x3aniac]

Originally Posted by Opie55

Right near the end of that clip it sounds like the same sound I have. Does it kind of sound like you are being followed by a small airplane?

Yes, around 9 secs to the end of the video the car was deaccelerating and sounds like you're in a plane.

[Opie55]

Originally Posted by x3aniac

Yes, around 9 secs to the end of the video the car was deaccelerating and sounds like you're in a plane.

I've had that sound for just about a year. I just recently noticed that when it is not really present it will appear if going around a left had curve putting a side load on the car. It is too even of a sound to be a bad bearing. Just listening to it for a year I am about 90% sure it is the rear differential.

[slowblackx3f25]

check the rear diff and make sure it is not leaking. My x3 had a leaking diff and it made a similar noise

[x3aniac]

Originally Posted by slowblackx3f25

check the rear diff and make sure it is not leaking. My x3 had a leaking diff and it made a similar noise

Would it be possible that I've damaged something while changing the rear shocks, I had to play with the half shafts or how those things are called that turn the wheels. Also half a year ago I got a drivetrain fault, that went way, I get some knocking, not through the brakes, but through the whole chassis, transmission, or maybe the diff now that you've mentioned it when coming to a full stop. But if it's making such noise and stopping abruptly I'd say there's a safe assumption that it might be the diff, which is causing the problem. I want to add that after I changed the rear shocks, I did a test drive, and near 80kmh there was such a bad sound, it sounded like a whole plane was about to take off in the car (it went away). Not sure if it came from the gearbox or the back of the car where the diff is located, but someone who's reading this will make a safe assumption. The car was at BMW for an oil change at the start of August, and they said that the diff is not leaking. Didn't mention anything about the abrupt stopping, even though we let them know about it.

[Bdavi011]

I am 100% having the same issue after replacing my rear shocks. I replaced them with OEM Sachs and I messed with the bolt that controls part of the alignment in the rear wheels and the car drove like ass until i got an alignment done. Car drove much better but this sound began like a bad rear wheel bearing and it is only on the rear right side.

It comes and goes, someday I hear, others times I don't. I doubt it's the rear diff since I've been on top of the fluid changes and when I was under the car, it was dry.

What doesn't make sense is the sound comes and goes. I figured if a part is bad, it just stays bad.

Either way, I can't do much to fix the issue, broke my arm and I'm waiting to address once I'm better.

[x3aniac]

Originally Posted by Bdavi011

I am 100% having the same issue after replacing my rear shocks. I replaced them with OEM Sachs and I messed with the bolt that controls part of the alignment in the rear wheels and the car drove like ass until i got an alignment done. Car drove much better but this sound began like a bad rear wheel bearing and it is only on the rear right side.

It comes and goes, someday I hear, others times I don't. I doubt it's the rear diff since I've been on top of the fluid changes and when I was under the car, it was dry.

What doesn't make sense is the sound comes and goes. I figured if a part is bad, it just stays bad.

Either way, I can't do much to fix the issue, broke my arm and I'm waiting to address once I'm better.

Well nice to meet you brother, I'm the bad left wheel bearing

Trying to find some alternatives to those chassis ears, maybe putting a phone up there or a GoPro, just thinking there will be a lot of wind noise. Not sure how is it with my X3, but the sound looks to be always there when driving faster.

I also replaced mine with Sachs, and reused some old parts, but everything is mostly new.

The problem is now that I want to remove the front wheels, to rotate the brake dust guards that broke on all 4 wheels. Don't even buy them new, the left side is interchangeable with the right side, there are holes made for the left and the right on one dust guard, so you can flip them over and their right for the other side. Went a bit off the track here, but my secret bolt key got fucked up by an Indie tire shop and I only managed to remove the wheels of the rear, so I'll have to come back to them for them to fix the problem.

Also that's a bummer for your arm. Come back stronger and healthier, dude!

[Opie55]

Originally Posted by Bdavi011

I am 100% having the same issue after replacing my rear shocks. I replaced them with OEM Sachs and I messed with the bolt that controls part of the alignment in the rear wheels and the car drove like ass until i got an alignment done. Car drove much better but this sound began like a bad rear wheel bearing and it is only on the rear right side.

It comes and goes, someday I hear, others times I don't. I doubt it's the rear diff since I've been on top of the fluid changes and when I was under the car, it was dry.

What doesn't make sense is the sound comes and goes. I figured if a part is bad, it just stays bad.

Either way, I can't do much to fix the issue, broke my arm and I'm waiting to address once I'm better.

Your logic is like mine - how can it be bad only sometimes. I just changed my diff fluid (no change), and it does not leak. But there are only so many things back there it can be. If it was a guibo, I'd expect it to be noisy all the time, and vibrate. A diff does not have to leak to start going bad. If any of us figures it out for sure, let's agree to post back here so we all know.

[Opie55]

I suppose a wheel bearing might make intermittent noise depending on how it's sitting in the races. I am not imagining that the noise changes if I am going around a sweeping left curve at a decent speed. It will get noticeably louder until I straighten the wheel and then it either gets less or goes silent. Sometimes even a lane change will cause that effect. I do not sense it coming from either right or left. When it's at it loudest, it really does sound like a miniature Cessna is behind my tailgate. The sound is a bit too smooth and not low enough to describe as a motorcycle following me - but it is in that ballpark.

[pungo]

Mechanics stethoscope may help isolate the location of the sound. I've been using one for decades and have found bad wheel bearings, bad diff bearings, bad idler pulley, bad alternator bearings, they really work well...

[x3aniac]

So I did a test drive today. Took some corners going about 80-100kmh at which the sound occurs. The sound didn't increase under left or right pressure. What are we thinking?

[Opie55]

Originally Posted by x3aniac

So I did a test drive today. Took some corners going about 80-100kmh at which the sound occurs. The sound didn't increase under left or right pressure. What are we thinking?

My guess is that if the issue is due to some sort of wear each car will be slightly different in how the noise manifests itself. I'm not saying mine does not do it in a straight line - it does - its' just that I also noticed that a left curve will typically make it louder. But not a right curve. The biggest mystery to me is why it does not do it all the time - or at least it is nearly inaudible. Then it will start all of a sudden. Mine also seems to do it more after I have been driving a while. It does not seem to be noticeable right after I start out. It will be one year tomorrow that mine started. I was passing a truck on the highway and thought the truck was using engine braking until I realized it was me.

[x3aniac]

Originally Posted by Opie55

Your logic is like mine - how can it be bad only sometimes. I just changed my diff fluid (no change), and it does not leak. But there are only so many things back there it can be. If it was a guibo, I'd expect it to be noisy all the time, and vibrate. A diff does not have to leak to start going bad. If any of us figures it out for sure, let's agree to post back here so we all know.

Looks like I was the fastest to return here. The car has been in the mechanic shop for a little less than 2 weeks. They took it for a test drive and diagnosed that the sound has been coming from the rear left wheel bearing. When it started almost a year ago it did sound like it was from the left wheel bearing, but then it progressed into what I thought was a bad rear differential.

Now onto some crazy stuff they discovered. The car was squeaking when it had reached the optimal temperature. Looked like nothing bad, generator, maybe the belt, you know "eh, it's probably the belt, the same old, will change out sometime". But no. The crankshaft damper, tensioner and the belt were shot. Had cracks all in the place, can't remember was it the tensioner or the damper, but they were loose, the type of loose, where if the screw would've turned one time, everything would have fallen apart kind. They said that the crankshaft could have spun because of it, some scary things A couple of months ago I changed out the rear shocks and haven't done the alignment. So I asked them to do it, there was minimal camber on the rear wheels, totally driveable, but the car still felt boat-like. Called me, and said the rear roll over strut was so shot, that they couldn't even unscrew it. So we agreed on heating it or doing whatever they got to do to remove it, and then changing it out for a new one. Not sure if they changed both sides, but oh well. Also I think they repumped the brakes, because there was already a service light on the dash.

The car is getting an alignment done and we will see if the rear wheel bearing fix was the one that caused the sound.

[Opie55]

How many miles on your car?

[x3aniac]

Originally Posted by Opie55

How many miles on your car?

180k miles, but the parts should be changed out around 120k.

[Opie55]

Originally Posted by x3aniac

180k miles, but the parts should be changed out around 120k.

My car has only 68k miles, and has been making the noise since probably 63k. Low miles is one reason I have been skeptical of a wheel bearing, but I'm coming to that conclusion.

[x3aniac]

Originally Posted by Opie55

My car has only 68k miles, and has been making the noise since probably 63k. Low miles is one reason I have been skeptical of a wheel bearing, but I'm coming to that conclusion.

Might as well just go to the mechanic shop for them to listen to the sound with their earphones.

[Opie55]

Originally Posted by x3aniac

Might as well just go to the mechanic shop for them to listen to the sound with their earphones.

I may, but I'm going to try and check it myself first. It's getting a bit louder, so I'm hoping if it's a bearing it will have some telltale play by now. If so, I don't need to guess. If not, I'll use a stethoscope and go from there. I'm a DIYer and don't like taking my car anywhere except for tires, alignment or paint. Have not paid an actual mechanic to work on a car since probably 2010, and that was only because I could not track down a weird noise. Neither did they.

[Opie55]

Did your repair fix the noise? I am finally going to break down and take it in. The sound itself seems to be a wheel bearing, but there is zero play and no obvious roughness or sound when I turn each wheel by hand. So to avoid just throwing parts at it I'll at least pay for a diagnosis. If they confirm a wheel bearing I'll probably replace it myself.

[Bdavi011]

Let us know if it fixes your noise!

So weird thing happened to my X3. I haven't driven or done anything to the car besides an oil change and the sound is 100% gone. I have no idea what it could have been but I'll probably try to get a look back there sometime soon since my arm is basically almost back to 100%. Appreciate the well wishes!

If I end up with any new findings I'll update the thread.

[Opie55]

Originally Posted by x3aniac

Looks like I was the fastest to return here. The car has been in the mechanic shop for a little less than 2 weeks. They took it for a test drive and diagnosed that the sound has been coming from the rear left wheel bearing. When it started almost a year ago it did sound like it was from the left wheel bearing, but then it progressed into what I thought was a bad rear differential.

Now onto some crazy stuff they discovered. The car was squeaking when it had reached the optimal temperature. Looked like nothing bad, generator, maybe the belt, you know "eh, it's probably the belt, the same old, will change out sometime". But no. The crankshaft damper, tensioner and the belt were shot. Had cracks all in the place, can't remember was it the tensioner or the damper, but they were loose, the type of loose, where if the screw would've turned one time, everything would have fallen apart kind. They said that the crankshaft could have spun because of it, some scary things A couple of months ago I changed out the rear shocks and haven't done the alignment. So I asked them to do it, there was minimal camber on the rear wheels, totally driveable, but the car still felt boat-like. Called me, and said the rear roll over strut was so shot, that they couldn't even unscrew it. So we agreed on heating it or doing whatever they got to do to remove it, and then changing it out for a new one. Not sure if they changed both sides, but oh well. Also I think they repumped the brakes, because there was already a service light on the dash.

The car is getting an alignment done and we will see if the rear wheel bearing fix was the one that caused the sound.

How about you - did the bearing fix it?