My 1990 Chevy truck has had a high pitched whistle that changes pitch with the engine speed. Open the hood, blip it, nothing, I just haven't had time to hunt for this thing.
Today doing ~50 mph my phone rings, I kill the radio to hear the call.
Whistle is gone.
Rats. Turn the radio on, yep, it's back. Blip the throttle, yep, up & down with rpm right out the speakers.
Any suggestion besides installing a high dollar stereo? This is a GM factory am/fm cassette unit.
Dan
have you changed anything?... I know my volvo does it pretty badly on the AM... I blame it on the Taylor plug wires...
Antenna filter can get rid of that. I'll look up instructions later. You cab probably make it. Out send me the parts. Oldschool electronics are fun.
Make sure your antenna wire isn't right by three distributor.
Wasn't that one of the original purposes of the condenser in the old (points) ignition systems? Seems to me there is a bad electronic filter someplace in the system. Don't know enough about the ignition system on that truck to even begin to suggest where to start though. Unless the replacement stereo has a built in filter the problem will reappear.
Spark plugs or plug wires would be my first guess.
My beemer does it on AM...but with the clutch pedal, nothing to do with rpm.
Rule#1 for finding odd noises: turn off radio. 
Noise wasn't that odd .....
emi
Might have a bad capcitor in the ignition. They are used even on pointless systems.
I've gotten feedback from an alternator. Pull the belt and start it up. If it's still there, you know it ain't the alternator
But it doesn't cost anything to try it.
Yeah, there's a capacitor in there somewhere to minimize that. Maybe at the coil, maybe at the alternator. Or there should be one.
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