Please point me in the right direction

[hershy573]

I'm trying to help my mother figure out what is going on with her truck. A while back I installed a Pioneer head unit in her 2005 GMC Sierra and it worked great. Now over a year later she has gone through 3 or 4 alternators in the last 6 months. No idea as to why that would be. Plus there is an annoying whining sound coming from under the hood when the radio is on, turn the radio off and the whining sound goes away. Lastly there are times when the radio will be on but no sound, but then you hit a bump and the music starts playing. I've been racking my brain for months trying to figure this out, so here I am asking those smarter than I to please help me. Thanks.