I have a Philips PC400 5.1 speaker system on my XP (SP3) PC. Speakers have worked fine for 18 months plus. Recently the subwoofer emits a continual pure low booming / low hum sound. (No crackling, no squealing)
I'm pretty sure this is just a sub woofer speaker problem as it makes the noise even when the PC is off!
I have not changed the position of the subwoofer or changed anything else in months.
Turning volume up/down has no effect on volume of this sound.
I have seen on another post to try to move cables - which ones there are loads!!
I have tried unplugging all the leads one at a time from the subwoofer to see which one is causing the hum. I have moved all the cables/transformers around, reseated all cables/jacks in the back of the PC ...
... and come to no firm conclusion yet!
I think it is an earthling problem as there have been no UFOs round here recently.
I will check PSU - thanks for all suggestions. Unfortunatly it isn't a figure of eight job though. Will post again after sorting it out.