Stange vibration in my M Roadster

[TZ <tzuehlke5@xxxxxxxxxxx>]

I have a '99 M Roadster with about 58,000 miles on it. I am experiencing an
intemittent problem that I would like to identify. During acceleration I'm fine, but if I
back off while staying in the same gear I get a vibration along with a little extra low
decible noise. Sitting in the car, it is hard to tell where it is coming from. This problem
has not happened during a downshift, and had not happened under torque or when
shifting up through the gears. Since it is intermmittent I have not taken it to a
mechanic but I ponder the following questions:

Wheel balancing problem? 'doubt it, not a problem at speed, just occasionally when I
back off in the same gear.

U-Joint Problem? maybe, it does sort of feel like it is along the drive train.

Guibo? Hmmm...this soon?

Insulation? I talked to one mechanic that said he has seen a piece of insulation
fall/interfere with the drive train on the Z3 series. I would never have thought of
that...

So, has anyone experienced this problem? Thanks, I need the piece of mind of knowing what kind of problem is brewing here.  Surely it isn't normal.

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