Diff or Exhaust noise?

Mon Sep 20, 2010 9:36 pm

Just noticed that at 60 km/h and over I'm getting a noise from the back of the Touring, a bit like a rumble but not like metal-on-metal grinding. and definitely not a whine. Car's a '88 320i.

I can't reproduce the noise while the car is static (revving the engine), only when driving, which is why I don't think it's a blowing exhaust. But I'm not sure what the process would be for testing the diff/bearings. Not heard anything like it before.

Any ideas?

Mon Sep 20, 2010 10:58 pm

Pewnie Most

Mon Sep 20, 2010 11:01 pm

Test the bearings by jacking up the rear and giving the wheel a bloody good shake. Any movement generally means you've got a shot bearing.

Tue Sep 21, 2010 12:30 am

Check that the heat shield above the rear box isn't loose. That can vibrate and make strange noises inside a touring.

Tue Sep 21, 2010 4:12 pm

Thanks for the tips so far. If I'm jacking up the rear end to check the bearings, what's the procedure for testing the diff while her arse is in the air too?

Wed Sep 22, 2010 3:00 pm

Right, got the back off the ground. No wheel shake at all, nothing loose or punctured in the exhaust system, and with the wheels turning to 60km/h (despite the car being static) this rumble starts up, and is present on overrun too. It sounds like I have a WW2 bomber under my car.

When turning one wheel by hand the other wheel does spin, but not immediately, and I can't feel any roughness or friction from either wheel; no whining, rubbing or grinding, just this persistent drone at speed.

So is this a shot differential? Or does it just need some oil?

Wed Oct 27, 2010 5:42 pm

Well, new diff on, a few hundred miles covered, and I'm still not sure.

It's not as noisy as it used to be, but there's still something there; or maybe I'm paranoid and the back ends of E30s are particularly rumbly all the time anyway. Either way, I'm sure it's not a wheel bearing, the heat shield is on tight, the exhaust isn't holed. Could it be a bearing in the prop shaft?