Metallic sounding "rattle" at startup

BMWfan73 · 12-20-2020, 03:50 PM

When I start up in the morning for the first time, I get a very quick metallic rattle or vibration sound. It sounds like it's coming from the rear of the car, maybe the exhaust? I've shaken it and everything seems to be tight, nothing loose or squeaking. Any ideas? 2015 X3 35i, 67k miles

raddoc · 12-20-2020, 04:47 PM

Bad catalytic converter or loose exhaust bracket...

BMWZ4 · 12-20-2020, 04:50 PM

Probably the exhaust bracket would be my guess as well

willywi · 12-20-2020, 06:21 PM

There is a vacuum line in the trunk that controls exhaust valve opening. You can try disconnecting that line and see if the rattle noise goes away.

BMWfan73 · 12-20-2020, 08:07 PM

Quote:

Originally Posted by willywi

There is a vacuum line in the trunk that controls exhaust valve opening. You can try disconnecting that line and see if the rattle noise goes away.

Noise is still there. Checked brackets and hangers and all is tight and secure.

willywi · 12-20-2020, 08:22 PM

Quote:

Originally Posted by BMWfan73

Noise is still there. Checked brackets and hangers and all is tight and secure.

Did you tried "Golf tee mod“？ I had exhaust rattle at cold start before and this mod solved the probelm.

BMWfan73 · 12-20-2020, 10:31 PM

Quote:

Originally Posted by willywi

Quote:

Originally Posted by BMWfan73

Noise is still there. Checked brackets and hangers and all is tight and secure.

Did you tried "Golf tee mod"？ I had exhaust rattle at cold start before and this mod solved the probelm.

Now that you mentioned it, I have done it but it never made that sound until recently, that's why I didn't associate it with the mod. I can reconnect things tomorrow and see if the rattle is still there or not.

6MT_Addict · 12-21-2020, 01:24 AM

It's probably just the exhaust flap in the tail pipe vibrating. It closes on cold start (stays open under no vacuum) and opens in certain conditions based around RPM.

It's probably rattling because the metal is cold and there's some extra tolerance because it has to operate with a fully heated up exhaust.

If you only hear it on a cold startup and not an at-temp startup then it points to this as one cause.

iagafoor · 12-26-2023, 01:52 PM

Wouldn’t there be any issue if we disconnect the electrical supply to the actuator which control open/close function of the valve located inside the exhaust pipe? I believe this sub system is made for purpose and if we disturb them.. may get into other issue? Living with annoying noise is better as compared to expensive repair coming from other end if any.

chris55552 · 01-18-2024, 12:16 AM

Also dont overlook a couple things, the emergency brake cable that runs along the uderbody has has a set of cable harness/supports that can rattle against the heat shields. My 35i starts up cold and grumpy but then settles down, the added vibration from being cold and grumpy could be causing enough vibration to rattle those items mentioned. I would pay attention to the sound and then try to mimmick it by tapping the heat shields and see if there is any similarities, that will help you narrow it down. Also another rattle I discovered on my vehicle that is common is with the brake disc heat shields, they are round and bend easy, alot of people have reported pebbles, rocks getting lodged between the shield and rotors and rattling, my front left shiled was bent and rubbing aginst the back of the wheel rotor while it was spinning so I reshaped it back and it solved my problem, although you are hearing this while the car is not in motion so thats not going to be it, but I would investigate the possibility of a pebble lodged behind the shield and any other loose part tapping the various heat shields on the underbody.

12-20-2020, 03:50 PM	#1
BMWfan73 Lord of Glencoe 34 Rep 108 Posts Drives: '15 xDrive35i M-Sport Join Date: Aug 2020 Location: Big Sky Country, MT iTrader: (0)	Metallic sounding "rattle" at startup When I start up in the morning for the first time, I get a very quick metallic rattle or vibration sound. It sounds like it's coming from the rear of the car, maybe the exhaust? I've shaken it and everything seems to be tight, nothing loose or squeaking. Any ideas? 2015 X3 35i, 67k miles __________________ (OO)=[][]=(OO)
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12-20-2020, 04:47 PM	#2
raddoc Private First Class 107 Rep 175 Posts Drives: X5,Model3,M240i Join Date: Jul 2019 Location: Tucson AZ iTrader: (0)	Bad catalytic converter or loose exhaust bracket...
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12-20-2020, 04:50 PM	#3
BMWZ4 Major General 1910 Rep 5,103 Posts Drives: '23 X1/'23 Allroad Progressiv Join Date: Apr 2010 Location: Toronto iTrader: (1)	Probably the exhaust bracket would be my guess as well __________________ '11 Z4 30i (retired);'11 X3 28i (retired); '15 M235i Stage 1 Dinan (recalled & crushed); '16 M235i Stage 3 Dinan (retired); '15 X3 28i (retired); '14 328i (retired), 2019 X3M40i (retired); Loaded '18 X1 (retired); Loaded '20 X3MC DG, Black/Tan Merino (retired); Loaded '23 X1 Cape York green and Red/Black interior; '23 Audi A4 Allroad Progressiv
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12-20-2020, 06:21 PM	#4
willywi Second Lieutenant 86 Rep 232 Posts Drives: BMW x3, BMW x5 Join Date: Jul 2018 Location: NY iTrader: (0)	There is a vacuum line in the trunk that controls exhaust valve opening. You can try disconnecting that line and see if the rattle noise goes away.
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12-21-2020, 01:24 AM	#8
6MT_Addict Captain 283 Rep 888 Posts Drives: 08 135i M Sport 6MT, 15 X3 35i Join Date: Feb 2013 Location: Edmonton iTrader: (2) Garage List 2008 BMW 135i [10.00]	It's probably just the exhaust flap in the tail pipe vibrating. It closes on cold start (stays open under no vacuum) and opens in certain conditions based around RPM. It's probably rattling because the metal is cold and there's some extra tolerance because it has to operate with a fully heated up exhaust. If you only hear it on a cold startup and not an at-temp startup then it points to this as one cause. __________________ 2015 Cosmic Blue Metallic Wrapped X3 35i ///M Sport Full 3M Vinyl Wrap \| Flat Black Grilles
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12-26-2023, 01:52 PM	#9
iagafoor IAG 2 Rep 37 Posts Drives: BMWX3 2013 Prem Packg AlpWhite Join Date: Sep 2013 Location: Toronto,Canada iTrader: (0)	Wouldn’t there be any issue if we disconnect the electrical supply to the actuator which control open/close function of the valve located inside the exhaust pipe? I believe this sub system is made for purpose and if we disturb them.. may get into other issue? Living with annoying noise is better as compared to expensive repair coming from other end if any.
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01-18-2024, 12:16 AM	#10
chris55552 Private 36 Rep 90 Posts Drives: 2017 BMW x3 35i Join Date: Jul 2023 Location: alexandra LA iTrader: (0)	Also dont overlook a couple things, the emergency brake cable that runs along the uderbody has has a set of cable harness/supports that can rattle against the heat shields. My 35i starts up cold and grumpy but then settles down, the added vibration from being cold and grumpy could be causing enough vibration to rattle those items mentioned. I would pay attention to the sound and then try to mimmick it by tapping the heat shields and see if there is any similarities, that will help you narrow it down. Also another rattle I discovered on my vehicle that is common is with the brake disc heat shields, they are round and bend easy, alot of people have reported pebbles, rocks getting lodged between the shield and rotors and rattling, my front left shiled was bent and rubbing aginst the back of the wheel rotor while it was spinning so I reshaped it back and it solved my problem, although you are hearing this while the car is not in motion so thats not going to be it, but I would investigate the possibility of a pebble lodged behind the shield and any other loose part tapping the various heat shields on the underbody.
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