I've got a 1993 Chevy K 1500 with the five seven just had a brand new rebuilt 4l60e put in it this morning. The radio began to work earlier today and I notice it has a squeal or whistling sound that corresponds with the RPM's of the engine. Would this be a case of a bad ground or should I be looking for something within the circuit that is shorting out?

 

I had this same exact problem in my jeep! In my case I had a cheap aftermarket headunit that the last owner put in it, sadly it didnt go away until i got a decent pioneer headunit. I never understood why it did that, maybe some sort of electric interference I guess... Beats me. But I can definetely say in my case it was the head unit, as soon as I replaced it and nothing else, the problem went away. Good luck though, at the worst spend 100$ and you can get something with a lot of features.

Edit: just realized how old this post is, but maybe you figured it out