After running on AC all summer, I just yesterday turned on the heater blower. When I did, I started to get an engine whine through the radio. The radio is an aftermarket head unit that runs through an amp in the trunk. The noise seems like it's coming from the amp, since the radio volume control doesn't change the noise at all.

The last time I heard this kind of noise (in another car), it was a bad ground. But this time, it only makes the noise when the heater blower is on. It's very clearly engine-related, since it changes with engine speed. But only when the blower is on.

I know I probably need new wires (got quite a shock the last time I set the timing ), but I would think that if that were the problem, the radio noise would be all the time.

It's very strange, and I can't think of why turning the blower on would cause engine electrical noise to come through the radio. Any ideas?

Blower motor brushes .. try a RF capacitor on the blower neg . the same you would see on the back of an alternator....

Thanks for the answer. Can you explain a little more? I'd like to really understand what's going on.

If the blower motor brushes are going bad, how does that couple electrical noise that's RPM-related?

Where can I find a capacitor of the right type?

And finally, can I get to the proper wire without going through the ordeal of getting through the dash to the blower motor?

Another idea is hose the blower motor with WD-40 through the outside air intake vent at/near the hood. I'd turn the blower motor on full blast then soak it from outside the car with WD-40 to help scrub them brushes thats what I'd do. And use the tube attachment on the can for reaching through the screen and getting close to blower motor.

It will not short any circuits, in fact I soak my alternator with the stuff as routine maintenance twice each year.