130i E87 - Mysterious Engine Noise, Rattle and Shake

[ironclaw]

Hi Folks,

I'm cross posting here to ask as wide an audience as possible with this issue. Its a 2007 E87 130i (Manual). Clutch and fly were done about 1800 miles ago and the car has about 114k miles on it.

Any thoughts or ideas welcome!

Initially:

Today, coming back from work, at about 100km/h the car began to develop a noise similar to a fan belt screech. However, when I had my foot on the accelerator (maintaining a constant speed of 100km/h) the noise stopped. However, as soon as I lifted, the noise grew and then subsided slowly as the car lost speed (Passing between the 100 and 80km/h bands(. If I pushed in the clutch completely, the noise fell away much quicker. If I accelerated, the noise disappeared above 100km/h. When stopped, the car had a very lumpy idle and would 'seek' continuously. The idle was so lumpy, it gently rocked the car.

However, no pulsating in the clutch pedal, no resistance to go. The clutch and fly were changed about ~2000km ago.

Now, the ringer, I drove it straight to my mechanic and he heard it coming. It sounded very sick. I switched off, went in for a brief chat and drove the car into the shop.

Nothing.

Its as if the car didn't have a thing wrong with it. I drove it home, horsing it if I'm honest, and nothing. Not a sound.

So, any ideas from anyone what possibly could have caused it? It can't be mechanical breakage, or it would show up continuously surely? My best guess, and its not based on anything, is a dirty injector / slight misfire, causing an inconsistent rotation and potentially throwing the fly off causing the wobble.

Update 1:

To report back, drove the car to work this morning and no issues until about 2 mins out (So engine up to temp, about 30km of driving in 80~100km/h traffic. Started to screech so I pulled over and turned off, then on the engine. Problem fixed, as fine for the next 5 mins to work.

It really has me incredibly confused as I can't trigger it on demand, nor does it appear to happen after anything specific. What makes it even weirder is that its a mechanical noise but it can be silenced by restarting the car.

Is there any system that would reset upon restart that would ultimately pull/push something back into place that would silence such a noise?

Update 2:

Car is now in the garage but an update:

- Car needs to be or almost up to temperature for it to start occurring.
- If you are accelerating, the noise will subside and fade. As you reach a steady speed, it will come back and start to build to a constant steady noise. Blip the throttle and it will subside momentarily.
- If you depress the clutch, even at 100km/h and hold it in, the noise will slowly subside (As if a wheel was slowly slowing down) Engage the clutch again and accelerate, and it will start to build once more.
- AC has no effect on the noise starting or stopping, on or off, it doesn't seem to cause it to happen any faster or slower.

Update 3:

Thanks folks.

Small update, its been with a mechanic for a number of days and they can't get the issue to appear, even with some long distance and mixed driving. The only difference we can see is that I would have the car in traffic a good deal more as opposed to his test drives which would be cruising.

Whats also got me stumped is the issue completely disappears when the car is restarted and only reoccurs after a significant amount of warm up / driving, but we can't identify any aspect of the system that the ECU would control to cause such a noise. My money is still on a pulley or similar, but the fact it stops when the car is restarted, surely rules out a pulley as its either broken or not broken, a restart won't fix that.

Original Thread: http://www.babybmw.net/viewtopic.php?f=11&t=94169

[mackeroni]

I am voting for belt or pulley bearings.

[juld0zer]

Your thread on the other site is the giveaway. This sounds very much like the rear main seal leak that the turbo 6s get.

http://www.1addicts.com/forums/showthread.php?t=1137592 Many similar threads all over the internet.

Question is - did they change the seal when they did the clutch? Some do it as precaution - one of those you might aswell things.

[juld0zer]

The sloppy idle is due to a vacuum leak because the crankcase is under vacuum, air is being drawn in via the leaky seal causing the whistle.

Im hoping that by depressing the clutch and easing the noise, that's just varying the crankcase vacuum due to change in revs rather than crankshaft endfloat tweaking the seal's lips back and forth forming a better seal