Need help solving a noise issue

[gearheadE30]

I know e30s make a lot of noise, and I have no issue with that. Unfortunately, I have something that definitely isn't right at the rear end. I don't think it causes an issue with driveability, and I can't feel it. I just had the subframe out to replace the bushings and the noise is still there.

It sounds almost like rubber on metal, with this light squealing noise. The brakes, throttle position, bumps in the road, and the handbrake have no effect on it whatsoever. The frequency/pitch varies directly with wheel speed, and is definitely coming from the rear of the car. It is very pronounced both inside and out. Volume seems equal on both sides of the car. The rear wheelbearings and brakes are brand new with less than 3000 miles on them.

Got any ideas?

[Collin]

Did you run the wheels on a lift or does it happen while driving?

I knew a guy who would complain about nearly the same thing, turns out it was just his brand new roof rack whistling. Any chance of high speed wind noise?

[gearheadE30]

I tried running the wheels on a lift multiple times, but I havn't been able to re-create the nose. It can't really be wind noise, as it starts at around 25 MPH, but remains until the car is stopped again. Gusts of wind don't affect it. I'm beginning to think it is something in the diff.

[ABuseO]

Does it have a pitch change respective to the acceleration of the car?

[ethirtydavid]

maybe the bearings in the center support on the drive shaft?

[gearheadE30]

Acceleration has no effect, only speed, so it can't be the ring/pinion in teh diff. I was thinking maybe a seal or a bearing.

The CSB is a pretty good guess. I've never really thought of it making noise, but it does have 200k miles on it, so it may be time for a replacement.

[ethirtydavid]

There not too bad to replace unless your exhaust is a welded 1 piece like my last e30 was.. then you have to unbolt at end of headers and drop out of the way.

other than that it's as easy as 3 nuts on the diff end and 3 bolts on guibo end of shaft.
just make sure when you separate shaft you line it back up the same. there are marks on it to get the splines aligned.

..you probably already know all this though

[TwoJ's]

Sticky caliper? Time to rebuild the ebrake?

[gearheadE30]

Calipers and ebrakes have both been rebuilt at about the same time I did the subframe.

ethirtydavid, the only thing I've heard about with the driveshaft that I'm not sure how to do is preload the CSB. I havn't searched yet, though, and I'm sure its on here somewhere.

[ethirtydavid]

Well so after you have removed the old and are installing the new CSB. Put the diff end of drive shaft in first and keep it there with those nuts, then tighten the guibo end - it will help if you stick the CSB to chassis during this part (but don't tighten yet, just there to hold the weight of shaft).
As you are tightening the CSB back to the chassis just pull it forward for preload (towards the engine) - you will see when you are down there.

Again, a really important part that you shouldn't overlook is marking the drive shaft. It's not a big deal at all but you will have vibrations if they do not go together the way they came out. I have pulled them apart on a couple of my last e30s and one was marked with little circle notches on each shaft, the other was not. I am not sure which one was stock.. One of those chalk pens will work well.

I just looked, here is an article you can follow:
http://www.pelicanparts.com/bmw/tech...ft_Bearing.htm

[gearheadE30]

Well, it seems to be the diff, actually. I'm pretty sure of this now, thanks to the help of a directional mic under the car ;). Looks like it's time to look into a new diff...

[SpecM]

Well, it seems to be the diff, actually. I'm pretty sure of this now, thanks to the help of a directional mic under the car ;). Looks like it's time to look into a new diff...

good you got that straitened

[gearheadE30]

I just put the car up on jackstands, and it definitely isn't the diff. In fact, I think it is a bad CV joint. I pulled the wheels off, and it sounds like a netallic screeching noise, and it is far too high pitched to be a bearing. The boot also appears to be torn up a bit, so there is probably water in there. This is a bit more involved to fix than the diff, though...

BTW the CSB is also bad, although that sounds more like a rumbling than a screech.