Strange noise in speedometer

[Dag Bøsterud]

My 1990 Audi 100 TQ Sport Exklusiv suddenly developed a strange sound.
The sound is a howling, quivering noise. I really cannot describe the sound
any better.
At first I thought this was a wheel bearing, but the sound seemed to be coming more from the center
of the car.

My speedometer has always worked perfectly, but I noticed that the speedometer
stops working when this strange sound goes away. Can an electronic speedometer
really make such a noise? Is this just a coincidence?

/Dag
1990 Audi 100 Turbo Quattro Sport Exklusiv
148200 miles