rcpilot

I replaced the hydrolic brake boster in a friends '91 Audi 100 and now I'm geting a high pitch tone from the radio.

One of the other things I'm going to do is swap the radio with another Audi radio per his request, which I tried to do while I was waiting for the correct "bomb" to come in. When the old "bomb" was out and before I got the new one in I had the same problem, but it went away after the "bomb" was installed and everything hooked up. Then a few days later I went out to swap the radios and I'm geting the high pitch tone from both radios. Every thing appears to be hooked up fine and working fine.

Sorry about the rambling. Any help would be nice, I need to get his car out of my garage so I can work on my '93 90s.

rooster 2

like a hydraulic brake booster can produce an RF signal that you could hear on the radio. Only something electrical like the alternator can do that. You may want to consider installing an RF interference "trap" on the power line to the radio, that may solve the problem.

Will Ng

If the car has the Bose system, and you were working under the dash...
there is a voltage noise filter located under the steering wheel. It's attached to/close to the steering column. It's an inductive filter, resembles a small transformer. You'll see some 16 GA red and brown wires connected to it.

Perhaps you bumped it while working. Make sure the grounds are good.

HTH.

rcpilot

I don't think that it is RF. It happens when the car is off or when running. But I'll take another look and make sure everything is connected correctly.

CARSNPLANES

and run the car with each of the units not spinning one by one. That will tell you which unit is the culprit.