Question Speakers whine after adding a higher powered subwoofer

Mar 1, 2022
My setup is as follows:

50+50+100W 2.1 Amp connected to my desktop PC via RCA to Aux cord. Connected to the amp are two passive Sony bookshelf speakers, and then for the sub is an active 75W Sony Sub. Setup has worked perfectly for years, both with line-out on my Desktop PC and the inbuilt Bluetooth radio. Never had any issues. Due to the sub not working after my landlord decided to unplug it from the wall, probably frying it, I had to find a new one--which leads me to my current problem.

I found a Rockville APM10 400W active subwoofer. Now this subwoofer connects and works fine with line-out on laptop, works fine with bluetooth connections.....but doesn't work properly with line-out on my desktop PC (which worked fine with the previous setup), with audio sounding crackly and staticy as well as producing a high pitched whine out of the bookshelf speakers. Turning down the volume in windows has no effect on the whine, but turning down the amp volume knob does.

Due to these complicated results, I cannot seem to determine the exact source of the problem. I assume it may be the soundcard of the desktop PC, given that it works fine on the laptop?

Any guidance would be greatly appreciated.

Thanks :)

EDIT: To clarify, if i unplug the rca from the sub the whining stops immediately, and then resumes when i plug it back in. This issue is not present when the amp is connected to my laptop aux or over bluetooth to my phone, rather only is the issue present when connected over aux to my desktop PC.

EDIT 2: It might be worthwhile to mention that the sub, amplifier and desktop pc were all connected to the same power strip which was unplugged.
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