Radio problems

For a while now, i have had proplems with excessive noise and squeals coming from my radio, and i'm finally getting close to a solution. Everytime the car was running, the radio would put out a loud hum, and occasionally a loud, sharp, squeal. It made it impossible to use the radio.(sensitive hearing)
I started by installing a noise suppressor, and it helped a little.I tried using a different alternator, but that did nothing. The next thing was to replace the plug wires, which did help a lot, but did not completely solve the problem. Later today I am going to use a different alternator again to see what that does, most likely I will rebuild an alternator when I get the money.
I figured i'd post this so if anyone else had a similar problem, they could try what I did.