feedback through speakers when scrolling

This is interesting, but annoying. Anytime I scroll in a browser window, or even just click and hold the scrollbar, I get a faint humming through my speakers. Has anyone else experienced this and does anyone have any idea how to fix it?

My relevant specs are:
Dell Optiplex 755
Intel(R) Core(TM)2 Quad  CPU   Q9550  @ 2.83GHz
pcm0: <Analog Devices AD1984 (Analog)> (play/rec) default
hw.physmem: 8410640384
Mixer vol      is currently set to  83:83
Mixer pcm      is currently set to 100:100
Mixer speaker  is currently set to 100:100
Mixer mic      is currently set to  67:67
Mixer mix      is currently set to 100:100
Mixer rec      is currently set to  72:72
Mixer igain    is currently set to   0:0
Mixer ogain    is currently set to 100:100
Recording source: mic
From my experience, this noise while scrolling is mostly heard from the elektronics of the monitor/TV when the contrast is set to a very high value.
Maybe your computer picks it up. I doubt is has something to do with your sound directly.

I would at first try to set mixer mic 0 to see if it's the mic picking it up.

And if that doesn't help or you don't want to turn it off, try lowering contrast and eventually brightness of your screen a little bit.
k.jacker, I'll give that a shot and post back.
dch, that sounds interesting. How do I disable GPU acceleration? I'm on FreeBSD 11.1-RELEASE #0 r321309.