Ok my radio just started doing it this morning. It worked fine until I tightened up the braided ground strap on the back of the head. I noticed the nut holding the ground strap was really loose. As soon as I tightened the strap the whine started. I undid the strap but the radio is still doing it. It only does it at low frequencies (104.1 and below). I have had other vehicles with alternator whine but it was in all frequencies. The unit is the stock 1989 tape deck/AM/FM radio. I have no aftermarket speakers or CB or anything that could casue interference. It kinda has me stumped. Any ideas??

 

Figured out the problem the other day. The black ground wire that plug straight into the back of the stock radio (not the antenna wire, the smaller wire with a female spade plug) was undone. Plugged it back in a its back to normal.

 

Thanks for the response on what fixed it, never ceases to amaze me the amount of stupid things that can cause a problem.