Weird mouse noise

My sound system is a Philips set as amp...Panasonic chip amps.
It is connected to the 3.5 mm output jack of my computer, and the computer is used as the DAC, playback etc.
Core2Duo, Gigabyte 41 series board, 2 GB RAM, Windows 7 ...it works well enough for me, I left Win 10 and came back to Win 7.

VLC player for video, Winamp 5.66 for audio.

The weird issue is there is a crackling noise when using the scroll wheel on mice, or even when using the slider on the side panel.
Checked with another mouse, and the up / down keys on the keyboard. Same result...

Any suggestions are welcome, this is a bit of a head scratcher for me.
Earthing is perfect.
 
To be clear you're saying the problem occurs when you scroll windows? Any sort of window and using either the mouse or keyboard? Does page up/down also have the same effect? I'd started by thinking USB but I'm inclining more toward software, though where you go with unpacking and lining up that particular can of worms is going to be a thankless task.

But it might be worth trying different USB sockets if you can. Also, how confident are you that your machine is clear of malware???

Do you recall when it started? Anything you were doing at about that time?
 
I cleaned the mouse, opened it out, removed dust and lint, it now scrolls only up, and there is no noise.
It is a Logitech mouse, and instead of a pot, it has a LED on one side of the wheel and a pick up on the other, and the wheel has slots, it is more reliable than the pots, where they wear out, sometimes there is wear between wheel and pot, so it slips, will not scroll.

I think I will reflow all the solder joints on the mouse PCB, and see what happens.