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cyclical throbbing (additional input)

Greetings again,

Some of you may recall a post I submitted a few weeks ago.

 Just put new Potenza RE930's, with 4 wheel alignment to replace worn
Pirelli P600 M&S on the '93 100csqw. New tires and alignment feel great.
However the absence of the wobble and tire noise, has highlighted a new

This faint vibration, or humming, occurs in cycles 1 sec on 1 sec off, and
only happens between 60 and 70 mph. There is no steering wheel shake. I have
tested on a variety of road surfaces.

Since then, I have had the following done:

Firestone Dealer which sold me the RE930's did:
a) re-check balance and rotate - hopefully the noise will move indicating a
bad tire... No change in noise or "location"
b) remove RE930's and test with another set of tires (Firestone Infinity -
really quiet T rated)...no change in noise or location so one would expect
that the RE930's are not the problem
c) replace the RE930 - of cource the noise is still there, and I'm now
thinking more expensive repairs like bearings or other drive train stuff.
d) Recommendation - take to Audi dealer to investigate further

Audi Dealership (Carousel in Mpls)
a) re-check balance and roate - again, no change
b) check for bent wheel - all wheels look good
c) on the hoist, check all bearings and drive train components (be ear?) -
no perceived noises when the car is on the rack
d) Final recommendation - wait until the noise gets worse.

So good news, I'm not out a lot of money yet, as no one seems to have a clue
what is the source of the problem. Any of you have an idea of what the
problem could be? Any ideas on what additional diagnostics I could perform?




Eric Billing
'93 100csqw - pearl - 58K miles - weird throbbing at 65+ mph