Question Surround System Channel Noise Issue

[altrefrain]

Hello, I've got some amplifier noise/interference that's driving me nuts. It's a high pitched whine with intermittent pulsing, like Morse code. I have a Midiland S4-8200 5.1 surround system that I've been using for the past 18 years for my PC. There's some noise coming from the Right and Surround Right channels. I've unplugged all inputs besides one speaker/cable, including the decoder input. I've unplugged all other power inputs into the power strip. The other three channels (center, left, surround left) don't exhibit the issue even when using the same speaker/cable. It gets louder when I tip the woofer/amp over at an angle. I even cut a short cable to ensure it wasn't interference from other cables bundled together. I turned off my phone to make sure it wasn't interference from that. Here's a link to a video that shows the sound. Any ideas on how to fix it? Or has my amp finally gone bad?

 

[americanaudiophile]

Speakers can't make static sounds without playing.
Sounds like noisy transistors or maybe a bad circuit board in the main unit. Given the age repair would be more expensive than replacement.