BMW mystery noise

Brake pad squealers? To easy I know.

I have no reason to suspect this, but if the parking brake shoes were dragging for a reason other than insufficient cable slack (something in the mechanism at the brake), then this hasn't been ruled out?

Mercifully, I'd think you'd at least be able to get it to change tone by applying a little parking brake.

Driveshaft center support bearing.

pointofdeparture wrote: Driveshaft center support bearing.

First thing that popped in my head.

^^ditto.

I would definitely check center support bearing. I had a guibo fail last year... That was an interesting driveline clunk.

Yep. Typical procedure is to drop the exhaust, then the heat shield to get at it.

FWIW it's a great time to freshen up all the shift linkage bushings and transmission mounts while you're in there, if you feel so inclined.

At least all those fasteners look really clean!

Doesn't sound like the support bearing to me since you can make it go away under acceleration or engine braking, the drive shaft would still be turning and you'd think it would change the pitch or make it quieter or louder but not go away. Does it do it when you are coasting down the road with the clutch pushed in and also in neutral? I realize the shaft would still spin but without power through it that should change the pitch and/or cause vibration if the csb is going out. I haven't gotten an alternative yet. Also I'm wrong a lot. I'll keep thinking about it though.

FWIW, I would think that the changing torsional load under accel/engine braking would be enough to make a sloppy center support bearing have an intermittent noise. Engines and diffs are mounted on rubber bushings, so keep in mind the whole drivetrain flexes differently under different circumstances. Acceleration and engine braking may load the mounts just enough to make the sound go away.

I had a Volvo 740 turbo with a problem very similar to this and it ended up being the CSB, which is why it was my suggestion.

I thought about a support bushing also, but it might be differential whine or transmission output bearing, but hopefully it is something stupid. I'd change the differential fluid while you are at it. To check the support bearing you can grab the sucker and see if it moves or a visual inspection might be easier said than done with exhaust placement. Look for torn rubber. I think you'd feel some wobble in the drive shaft but maybe not. For what a support bearing does I couldn't imagine it making an audible noise unless it is really bad. Too bad you couldn't get it on a dyno with an inspection camera and recorder.

Wonder if it is like the mercedes where they used a centering bushing that is pressed into the drive shaft. The original design only used rubber and would allow the driveshaft to wiggle around creating a bit of a wobble and stressing out the flex disc. There must have been an update because the new design uses a brass bushing and rubber dust seal. A bitch to install, you have to drill a hole in it and beat it out. Good luck, keep us posted! I hate weird noises.

On a somewhat related note, I think my driveshaft support bearing is going out because I have felt a driveline twist and wobble under hard acceleration a couple of times.

That's what mercedes calls a driveshaft support bearing. Basically supports the driveshaft over the length between the transmission and differential, I had to replace that also. Mercedes uses a centering bushing on both sides of the drive shaft that is pressed into the driveshaft and centers the driveshaft to the transmission output yoke and differential input yoke, looks like this. Good luck Woody, you'll get it fixed one way or the other.

I chased this noise around on my E46 for a while -- faint, high pitched, intermittent squeal. Always the same pitch, regardless of speed. Sounded like a dragging brake pad or parking brake drum. Finally...it did it once sitting still and out of gear. It's the fuel pump in my case. I chose not to replace it as it is apparently a common noise.

An no...it doesn't sound like normal fuel pump noise. It had me thrown. I chased all the same stuff -- new brake pads, overhauled calipers, adjusted and lubed the parking brake drums, etc etc.

I don't know if these cars have a PWM fuel pump or not, but it almost never makes the noise unless its hot and the engine is under some load. Like cruising down the interstate.

I'm with those voting it's the center support bearing.

If it's still making the noise after replacement, I would look at the motor mounts. The E36 mounts wear out faster than one would expect. Usually you'd get noise at throttle application or engine braking with that. But if just one is bad, and it's allowing the motor to tip back when the engine is in a steady power state, that could be angling the drive line enough to cause a squeal. Adding power or engine braking could be twisting the motor over to the good mount.

Make sure you preload it when installing it. If you have the manual check the instructions but off the top of my head you need to push towards the back of the car about 1/2" before tightening to the body.

If you dont have the manual, let me know and I can check and make sure what I said above is correct.

At any rate, let us know asap. the suspense is killing me.

Woody wrote: I have the Bentley manual. I'll double check, but I think it said preload it forward 1mm.

I am glad I was close lol

Maybe there is no fix?

http://www.bimmerfest.com/forums/showthread.php?t=155818

I always thought most irritating noises in a BMW came from the drivers seat

Kidding aside, I'm curious to see what it is when you find it.

I'm starting to like Tyler H's idea of it being the fuel pump. Thinking with the additional noise of acceleration and engine braking that it masks the noise under those conditions. Also Spoolpigeon is right. There is a reason We are the opposite of porcupines. ;)

I hear ya Woody. and I'm completely out of ideas at this point. I hope you figure it out soon. Wishing you luck!

Well, if the noise changes, or hopefully goes away, when you change the fluid at least you know it's the rear end at that point.

If it's back on the wheels, you could try killing the car and coasting to see if it is still there? How loud are we talking about? We're probably all more sensitive than most when it comes to automotive mystery noises, but is this an OCD thing?

My darling wife probably wouldn't notice if a con-rod were sticking out of the block unless the car stopped.

Dumb question: Did you check the level/condition of the gear oil? At this point, you've ruled out just about everything but a bearing somewhere in the transmission of rear end. No bent brake rotor dust shields? The kill it and coast will help rule out that weird fuel pump noise. My car started doing the same thing a couple of times on the way to work. In my case, it's definitely there, but it's not 'oh my god something's about to break' loud. I.e. My wife would never notice it, but I'm OCD.