Engine noise on radio 1989 C3500

[nickeliah1]

Hey all,

 

Having trouble with a whining noise coming from the stock radio on my 1989 c3500 (454). The pitch of the whine varies as I push down on the gas pedal, which leads me to suspect the alternator. The sound doesn't "pop" which people say could be the spark plugs.

 

I downloaded the "electrical diagrams and diagnosis manual" and inspected and cleaned all the grounds. Which improved the whine but its still there and painful to hear all the time.

See the spreadsheet I made with the grounds here: https://docs.google.com/spreadsheets/d/1XfEkczFd3AscQhc9hYyHzsz_VIDP9AfXB_G0Hb8vUKg/edit?usp=sharing

 

Any ideas on what could be causing it?

Should I try replacing the alternator? (alternator doesn't appear to be the original - has a Napa auto sticker)