Radio buzz from engine (archive)

My radio sometimes buzzes at a frequency proportional to the engine RPM. The buzz it at a constant volume- it's the same regardless of the volume setting. It's there whether the mute is on or off. It's there if I'm using the CD player or listening to the radio. If I turn the radio off, then on, the buzzing remains, but if I turn the car off, then restart it, the buzz may be gone.

The car is an '86 535i. The radio is a Blaupunkt Portland CM85, and it controls a Sony CD changer in the trunk. The rest of the sound system is the BMW Sound System that came with the car, including the amp in the trunk.

I removed the manual fader when I installed the Blaupunkt. I also installed a signal attenuator from Crutchfield to go between the head unit outputs and the amp. Aside from that, the wiring is stock.

Suspecting a bad connection, I tried unplugging and reconnecting the amp; the buzzing remains.

I'm trying to avoid going on an exhaustive glitch hunt. Has anyone already gone through this and can cut to the chase?

Follow Ups:

Re: Radio buzz from engine artie 23:03 1/28/2001 (0)

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