1997 E36 Back End "Wobble"

In the last two weeks or so, my 1997 E36 has started to "wag it's tail."
From about 15-20 mph, the car wobbles...not very technical, I know, but
that's the best way to describe it. It feels like one of the wheels is eccentric, like those little kids toys where the center of the wheel isn't where the axel is mounted. There is very limited feedback through the steering wheel, so I suspect the back end, but I'm not positive.
It appears to be some kind of resonance between the drivetrain and the suspension, since it goes away above 20 mph, comes back around 35-40, then is gone until you get up over 65. It gets really bad at 80+. It scales with wheel speed, not engine RPM, so I know it's something downstream of the transmission.
At first I thought I'd thrown a balance weight off one of the wheels, but that shouldn't have so pronounced an effect at low speeds (I think). I haven't had any collisions or bumps with anything that might have bent anything. The only thing that's a little off with the car at the moment is my rear tires are overdue for replacement (they're starting to look like racing slicks), but it's uniform wear without any flat spots or anything like that.
Any ideas? Wheel bearing?
Thanks, Tom.
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On Tue, 14 Nov 2006 14:46:12 GMT, "Tom Sanderson"

Well it could be many things from a buckled wheel, worn rear bearing or shot damper, but my immediate thought is the damper top mounts. They're quite well known for going, and can make the back end feel incredibly vague when they're worn.
They're not expensive, and they're very easy to change (unless your boot/trunk is as full of stuff as mine was at the time!).
Dodgy.
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Tom Sanderson wrote:

Drive shaft misbalanced? guibo shot?
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Could be any number of things. Might be a bad suspension bushing or broken link.
Have someone else drive your car while you follow behind, and watch how things move around as it corners and goes over bumps or dips.
Tom Sanderson wrote:

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My E36 suffered from worn suspension bushes on the rear trailing arms. It still felt stiff cos of the mass of the car, but it made banging sounds. You could see it was worn as the wheels had quite a camber and the tyres we wearing funny. The handling didn't change notably when they were replaced, that is to say the wear did not give handling problems.
Rex B wrote:

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The most common fault that causes the symptom you describe is tread separation on one of the tires. If you get your tires rotated so that your back tires are placed on the front it will also cause the steering to pull to one side. If you let it go for a while longer you may also start to hear a slapping sound at high speeds.

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An E36 I bought recently did something similar. It reminded me of my old E36 318iS after it was mildly rear ended by a blind woman in a Renault. In both cases a four wheel alignment fixed it, the rear trailing arms were slightly out of position.
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