Hissing/dragging mystery noise from rear end, stumped!

[Deutschbag]

Just acquired a new '91 325ic for my lady and I'm having trouble diagnosing a noise in the rear end. It *kinda* sounds like a brake caliper dragging, but I've jacked up the car, threw it in neutral and spun the wheels and it doesn't feel like they're dragging at all. The sound increases with speed, beginning at about 10mph. It doesn't seem to be any louder when turning left or right, so I don't suspect wheel bearings. I thought maybe like brake dust shield but I can't see anything interfering back there.

The PO states that he did the rear brakes not too long ago, and the e-brake doesn't work very well at all, if that could be part of the issue. Also, it's an automatic if that makes a difference (never owned an automatic anything, new territory for me). This one has me completely stumped, I thought for sure it was the brakes. Could I have a seized caliper even though it's not actively stopping the wheel from turning? The sound doesn't change when applying the brakes.

TIA for the help, fellas :)

[immajackuup]

having the same problem here too.

[vpilarrt]

Check the emergency brakes. Could be they're mal-adjusted and one of the shoes is rubbing its drum.

[ACHTUNG]

Could it be the diff going bad?

[MTechnikII]

same problem here too , I was told it's the bearing on the diff, and it's not easy to replace,
Henry

[FLG]

While driving, does it go away/change pitch if you apply the e-brake a bit?

[series88]

could be the diff or possibly wheel bearings?

[Deutschbag]

I will check to see if the noise goes away with a light application of the e-brake, that's a good idea. I was thinking maybe the diff too, but how would I check that? I was gonna do a diff gear oil replacement just for the hell of it in my new-to-me car maintenance, so I'll see if it helps.

Other than swapping the diff oil, is there some kind of way to check the condition of the rear diff? OH and lastly, I did put the car into gear when it was in the air and gave it a little gas, probably had the wheels moving about 20mph and I couldn't really hear the noise. So perhaps it is wheel bearings, but the noise doesn't increase when turning left or right, so that's why I'm struggling with this.

[MTechnikII]

swapping of the diff oil won't fix it, have tryed it.
the bearing is for the input shaft and it's inside the diff,
I don't see any easy fix for this other than a diff replacement( I've also heard the used diffs might have a bad bearing as well)
the hissing does not start till up to 10 15 MPH when you roll bellow this speed there is no hissing , the wheel bearing will make a different noise and will do it from the start.
My E30 is a convertible, and I only hear the hissing when the top is up.
Henry

[Deutschbag]

Damnit. You're most likely right, I just did the e-brake test last night and the noise didn't change. Actually as it turns out, the e-brake is HORRIBLY adjusted. With a firm pull of the e-brake handle, I can still spin the rear wheels by hand without too much trouble.

@MTechnikII, how long have you been driving with this bad input shaft bearing? I have a whole host of other maintenance to do first, she can't afford a new diff at this juncture and she commutes approx. 50 miles every day (pasadena to santa monica)

EDIT: Oh and I wonder if this is a non-LSD diff problem? My old 318is never had the issue, and my buddy's 325is is fine, but this is the first BMW I've tinkered with that had an open diff.

[MTechnikII]

I've owned the car since April 2003 and it has hissed ever since I got the car, in the beginning I thought something is rubbing against a shaft or drive shaft, oh easy fix I'll fix it soon, but when I didn't find anything rubbing or touching I was told its inside the diff, so I just turn the radio up and the hissing goes away :)
Non LSD diff on cabrios
Henry
the car has over 220kmiles,
it's not the Mtech I own , the Mtech is quiet no hissing , it has about 130kmiles

[Deutschbag]

Haha okay cool. That was my woman's solution to the problem, day 2 she got a new stereo installed :D But good to know it's not a huge problem, just kind of annoying because of my OCD with cars. Thanks man :)

[long tall eta]

you can get a used open diff for a couple fish heads and a bowl of rice.

[MoreMayhem]

Non LSD diff on cabrios

Does this mean that the LSD diff on my cabrio isn't original? I received zero history on the car (auction) and it is a 3.73 LSD.

BTW: mine makes this noise too.

[MTechnikII]

as far as I know the automatic cabrios came with 4.10 open diffs, there might be other difes on different year models,
mine is a 1991 plastic bumper automatic
Henry