Two (related?) sounds: 1) high pitch squeal right rear; 2) low humming center

m@rco · 06-20-2023, 10:13 AM

Grateful for your thoughts about what could be going on...

328i 2007 6MT 167,000mls - well maintained.

I recently noticed two types of sounds:

1. A high pitch squeal, not constant, but synchronous with the wheel rotation, coming from rear right wheel. However, the squeal only happens when in gear. The sound already occurs when driving in 1st gear at idling speed (800rpm or so). Taking left or right corners (on empty parking lot) do not change the sound, suggesting that it is not a wheel bearing issue. The sound somewhat resembles a high pitch "bird twitter": "tweet, tweet, tweet, or swoosh, swoosh, swoosh, etc.". It feels - but i'm not positive - as if the tweets come at a frequency fast that the wheel makes a full rotation, suggesting it has to do with the drive shaft. However, when I press the clutch pedal and the clutch is not engaged (or engage shifter in 'neutral') the sound disappears. The sound is not present when I drive up a steep hill in first gear suggesting that the 'natural move under angle or load' impacts the touching surfaces that produce the sound. The sound is present when in reverse though. Lastly, when driving in 1st gear with parking brake engaged or left foot on brake, the sound is still present. The latter suggesting that it is not a sticking (parking) brake issue. What could this be?

2. A low humming sound, constant, only at ~63mph, coming from the centre back of the car. This sound is present in all gears: 6th, 5th, 4th, even 3rd. But only present when 'under light/medium load'. As soon as you lift your foot of the accelerator or press clutch pedal (drive train not connected to engine), the sound disappears. The car experiences practically zero vibrations at whatever speed, save for the typical, however minute, tremble in the steering wheel at ~50mph, most likely a result of not perfectly balanced front wheels (I don't always rebalance after summer/winter setup change). I'm pretty confident that this has nothing to do with the humming sound. My wife first thought is was a car with loud/open pipes driving near to us, in stead of it being our own car...

It is difficult to conclude that sound 1 and sound 2 are related. At 63mph the wind overtakes the sound of sound 1...

For what it's worth, good to notice that the car otherwise drives perfectly. It drives perfectly straight. At (very) hard braking from 100mph to 40mph it decelerates in a perfectly straight line.

Lastly, and this COULD have triggered the sound(s) above, my good and trusted friend borrowed my car one week before I noticed the squeal. I know... Anyway, he admitted to have - unfortunately - missed a speed bump at night and hit it pretty hard. However, he was more complaining about the absent road warnings than about the tough encounter itself. Also, because the car seemed to run perfectly fine afterwards. Could this impact have caused a bearing or universal joint failure?

Grateful for your thoughts: what part is showing end of life time?!? center drive shaft bearing, universal joint, wheel bearing, brake, bent suspension parts, differential, ... Are sound 1 and sound 2 related or is it purely coincidental? Sound 2 could have been around longer; I just hadn't picked it up because I typically drive faster than 63mph on the interstate...

Thank you for your combined brain power.

m@rco · 06-28-2023, 02:23 PM

Quick status update.

I brought the car in to a great (ex-BMW) mechanic, based in Southborough, MA. He took the stethoscope out while his colleague was "driving" the car on the lift. Long story short: center bearing was the culprit. I could definitely feel that it was no longer rotating smoothly, in fact, required quite some force to get through a certain portion on one complete rotation.

I had it replaced and both sounds are gone. I was worried about the universal joints (which would require a complete new driveshaft) but these seem to be operating fine.

Excellent service and very reasonable price while getting urgent repair done (drove car to NYC one day later for shipping overseas...).

m@rco · 09-22-2023, 06:15 AM

New update...

New (or changed) sounds - unfortunately. No deep humming sound but I now hear a high(er) pitched squeal that (somewhat) resembles the sound of the wind inside/around your house during a heavy storm... The sound comes from the rear, right end, and manifests itself:
- after a cold start (bearings are cold);
- only at speeds between 32mph (50kph) and 45mph (70kph);
- reduces and then disappears after driving for about 2 mls (3km);
- does not reappear as long as the engine/bearings are hot/warm.

Any ideas? Wheel bearing? Differential? Anything else? I have yet to "perform a bearing test" through a quick jerk on the steering wheel.

Thank you for your collective thinking!

06-20-2023, 10:13 AM	#1
m@rco First Lieutenant 23 Rep 322 Posts Drives: '20 540i; '07 328i; '03 R1150R Join Date: Dec 2009 Location: Boston iTrader: (0)	Two (related?) sounds: 1) high pitch squeal right rear; 2) low humming center Grateful for your thoughts about what could be going on... 328i 2007 6MT 167,000mls - well maintained. I recently noticed two types of sounds: 1. A high pitch squeal, not constant, but synchronous with the wheel rotation, coming from rear right wheel. However, the squeal only happens when in gear. The sound already occurs when driving in 1st gear at idling speed (800rpm or so). Taking left or right corners (on empty parking lot) do not change the sound, suggesting that it is not a wheel bearing issue. The sound somewhat resembles a high pitch "bird twitter": "tweet, tweet, tweet, or swoosh, swoosh, swoosh, etc.". It feels - but i'm not positive - as if the tweets come at a frequency fast that the wheel makes a full rotation, suggesting it has to do with the drive shaft. However, when I press the clutch pedal and the clutch is not engaged (or engage shifter in 'neutral') the sound disappears. The sound is not present when I drive up a steep hill in first gear suggesting that the 'natural move under angle or load' impacts the touching surfaces that produce the sound. The sound is present when in reverse though. Lastly, when driving in 1st gear with parking brake engaged or left foot on brake, the sound is still present. The latter suggesting that it is not a sticking (parking) brake issue. What could this be? 2. A low humming sound, constant, only at ~63mph, coming from the centre back of the car. This sound is present in all gears: 6th, 5th, 4th, even 3rd. But only present when 'under light/medium load'. As soon as you lift your foot of the accelerator or press clutch pedal (drive train not connected to engine), the sound disappears. The car experiences practically zero vibrations at whatever speed, save for the typical, however minute, tremble in the steering wheel at ~50mph, most likely a result of not perfectly balanced front wheels (I don't always rebalance after summer/winter setup change). I'm pretty confident that this has nothing to do with the humming sound. My wife first thought is was a car with loud/open pipes driving near to us, in stead of it being our own car... It is difficult to conclude that sound 1 and sound 2 are related. At 63mph the wind overtakes the sound of sound 1... For what it's worth, good to notice that the car otherwise drives perfectly. It drives perfectly straight. At (very) hard braking from 100mph to 40mph it decelerates in a perfectly straight line. Lastly, and this COULD have triggered the sound(s) above, my good and trusted friend borrowed my car one week before I noticed the squeal. I know... Anyway, he admitted to have - unfortunately - missed a speed bump at night and hit it pretty hard. However, he was more complaining about the absent road warnings than about the tough encounter itself. Also, because the car seemed to run perfectly fine afterwards. Could this impact have caused a bearing or universal joint failure? Grateful for your thoughts: what part is showing end of life time?!? center drive shaft bearing, universal joint, wheel bearing, brake, bent suspension parts, differential, ... Are sound 1 and sound 2 related or is it purely coincidental? Sound 2 could have been around longer; I just hadn't picked it up because I typically drive faster than 63mph on the interstate... Thank you for your combined brain power. Last edited by m@rco; 06-20-2023 at 01:18 PM..
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06-28-2023, 02:23 PM	#2
m@rco First Lieutenant 23 Rep 322 Posts Drives: '20 540i; '07 328i; '03 R1150R Join Date: Dec 2009 Location: Boston iTrader: (0)	Quick status update. I brought the car in to a great (ex-BMW) mechanic, based in Southborough, MA. He took the stethoscope out while his colleague was "driving" the car on the lift. Long story short: center bearing was the culprit. I could definitely feel that it was no longer rotating smoothly, in fact, required quite some force to get through a certain portion on one complete rotation. I had it replaced and both sounds are gone. I was worried about the universal joints (which would require a complete new driveshaft) but these seem to be operating fine. Excellent service and very reasonable price while getting urgent repair done (drove car to NYC one day later for shipping overseas...).
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09-22-2023, 06:15 AM	#3
m@rco First Lieutenant 23 Rep 322 Posts Drives: '20 540i; '07 328i; '03 R1150R Join Date: Dec 2009 Location: Boston iTrader: (0)	New update... New (or changed) sounds - unfortunately. No deep humming sound but I now hear a high(er) pitched squeal that (somewhat) resembles the sound of the wind inside/around your house during a heavy storm... The sound comes from the rear, right end, and manifests itself: - after a cold start (bearings are cold); - only at speeds between 32mph (50kph) and 45mph (70kph); - reduces and then disappears after driving for about 2 mls (3km); - does not reappear as long as the engine/bearings are hot/warm. Any ideas? Wheel bearing? Differential? Anything else? I have yet to "perform a bearing test" through a quick jerk on the steering wheel. Thank you for your collective thinking!
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