90 c1500 all original, the original radio is picking up engine noise- whinning noise, it practacally went away when the alternator went out, is there a noise filter somewhere that has gone bad? It's a new toy to me and not sure how long it has been doing it.

 

sounds like a bad ground problem.....alternator whine is always a bad ground.....without getting technical about it.basiclly the radio or the alternator is trying to find a ground....The problem is usually found in the chassis ground straps

 

Those amplifiers in the late 80's to mid 90's trucks go bad and will make that noise. They are pricey if you can even find a good one. The best way to fix it is put in an aftermarket radio - unfortunately.