RedCharles wrote on 2020-11-26, 20:20:

I've narrowed down my speaker hum to my XP machine. If I disconnect the power cable to the XP machine, the speaker hum goes away. That PC is connected to the receiver through three 3.5mm to RCA cables. Merely touching the computer case with the 3.5 mm jack will cause background hum in my speakers.

I'm concerned about the power supply. I replaced the fans inside. I'm wondering if I did something. I'm wondering why the computer case is...outputting a 60hz signal. Should I be concerned about the power supply? Leakage?

There's a product some people call a power conditioner. A hum X costs 60-80 bucks. I was considering buying it.

Probably a ground loop and not a PSU issue . Searching for "ground loop" on vogons and/or in your favorite search engine should get you some useful ideas .