Whistling/whining noise from the back

[Kylemontanaro]

It's me again. The good news is that my 1992 850 has passed the strict German inspections and I'll be registering it later this week.

I have a weird whistling/whiny noise that comes on while driving (and no, the missus was not on board). The noise tends to start at random while accelerating, some days it does, some days it doesn't and stops once I slow down to almost a complete stop. It's not very loud and to me it sounds like it was coming from under the rear RH pax seat although once I had a passenger who said it was coming from below the rear LH seat. I've pulled the RH seat and the access panel to the fuel tank and it looks like no-one has yet been in there, so I'm already planning to replace the pumps and fuel lines out of an abundance of caution.

I wanted to blame the fuel pumps, but when it started, the noise would still keep going when I coasted with the engine on idle, so it's very puzzling. Oh and it slightly increase in frequency if I rev the engine, but again, it is not consistent, most of the time it's not there.

Anyone had anything similar happening?

[LappingLuke]

YESSS!! I experienced the exact same symptoms you describe. Believe it or not, for me it was the driveshaft center support bearing. I exhausted every other possibility before replacing the entire driveshaft with new. When I spun the CSB by hand, it screamed just like my video in the attached thread.

https://www.bimmerforums.com/forum/s...l-tank-related

[Kylemontanaro]

Oh no! If that's the case on mine that's terrible cause the last owner had a brand new OEM exhaust fitted all the way from front to back and I'd hate to drop that.
Is there a way to check it without taking off too much? Judging by how quiet and random mine still is, it probably won't give me any noticeable radial play.

[LappingLuke]

It's not that bad to drop the exhaust. I have made so many major improvements to my car since I bought it and replacing the driveshaft to fix this horrible, incessant noise is right up there with plugging in an injector that wasn't plugged in and rebuilding my shifter assembly.

The evap/charcoal canister valve you noted from my other thread is not your problem. If you're having fuel tank pressure problems (I was having this problem as well) then you may want to get that valve but it won't fix your CSB sqeak.

[Kylemontanaro]

Actually, I did notice the whooshing sound a bit when I went to refuel last time, but I was almost sure it had nothing to do with the whiny noise because it was dependent on the car actually moving. I just got this 850, so multiple issues at once are to be expected. Current priority is most of the rubber bushings at the forward and rear axles and a full service with all fluids.

Thanks for pointing the CSB out, would not have occurred to me so quickly!

[Kylemontanaro]

How was the state of the CSB for most of you when you pulled it out to replace it? Was it just the bearing that was shot, or was the complete centre mount (i mean the rubber) destroyed?
@LappingLuke Did your CSB also come and go, so to speak? Mine was squeaking at random the first week after I registered it, then it went away for a while, and now it's back with a bit more consistency.

[LappingLuke]

Yes the noise was totally unpredictable and I had zero control over it other than I could stop it by stopping the car. Once above 5mph again it was a total crapshoot as to if the noise would start immediately or some time later.

As for the csb itself visually it looked pretty fine but spun too freely as a worn bearing does and it squealed at me when I spun it as fast as I could.

[Kylemontanaro]

Thanks for the info. I meant the rubber itself, was it cracked?

[LappingLuke]

Nothing was visually bad enough to catch my eye.

[dragon850]

Is the noise there on idle? I just replaced a "howling" fuel pump assembly on one of the cars, cause was a kinked incorrect fuel line below the pressure regulator. It wore out the pumps running pressures over 55psi and the howling noise started !

[Kylemontanaro]

The noise is independent of engine speed, I tried coasting on idle and the noise continues. It stopped once it drops below ~5km/h.