[JamesInSJ]

I picked up a 2013 xdrive 28i earlier this year, ~115k miles. Timing chain was replaced by dealer before they sold it to me. I know the 4-banger is a bit different, but I have a vibration/hum under load at 2500+ rpm, most pronounced in the 3-4000rpm range. In neutral, whether at speed or parked, I can rev the engine and everything is fine.

Thoughts on which of the following is likely? I hate throwing parts at it...but might have to start somewhere.

1) Engine mounts? My #1 guess. Current mounts look fine, but I know at 10 years & >100k miles, it could easily be these. Wish it wasn't such a PITA to swap these or I would have already done it before posting here.

2) Harmonic balancer? I don't see any obvious damage/wear, but it does have a *slight* wobble to it. Since it only vibrates under load, I think that excludes this. I shared a video of it on another forum and they said the amount of wobble (maybe 1mm) was pretty normal on many cars.

3) Tcase support? I just had this down for a Tcase fluid replacement, and looked good. All rubber still intact and connected.

4) Are there any transmission mounts to consider on this car?

5) front or rear driveshafts? While I was doing Tcase/tranny fluid/diff fluid, I pushed, moved, etc. the driveshafts and CV joints all looked and felt excellent. Very little play noticeable anywhere.

[ultimate-tester]

Did you already eliminate brakes and tires as options? Since it only happens while in D, I would eliminate stuff like motor mounts and indeed start looking at things that are moving when driving (and not when in neutral)

Have someone sit in the back while you drive, try to locate the sound. From there you can explore the options and start checking things.

[JamesInSJ]

Originally Posted by ultimate-tester

Did you already eliminate brakes and tires as options? Since it only happens while in D, I would eliminate stuff like motor mounts and indeed start looking at things that are moving when driving (and not when in neutral)

Have someone sit in the back while you drive, try to locate the sound. From there you can explore the options and start checking things.

It's entirely engine rpm related so that should eliminate brakes/tires. It's also not speed related so I would guess that eliminates drivetrain (e.g. guibo's or whatever) except for the transmission...so I'm left with engine and transmission and related mounting of those. Back-seat riding is a good idea...it could be as simple as the exhaust being pushed up against something rather than directly at the engine itself.