I've been getting an annoying whining noise over my studio monitors due to my optical mouse. As I move the mouse the pitch of the whine changes, particularly when I change the angle at which its sitting on the mouse pad. So basically whenever I move the mouse it fluctuates a whole lot.
I've trying to get rid of it, but so far no success. I used to have my mac (a 2009 Mac Pro) plugged directly into my speakers via the mac's unbalanced line out jack, and the speakers were plugged into the same power strip as my mac. So I figured the issue was unclean electricity plus unbalanced audio.
I have since gotten a firewire audio interface with balanced outs (a MOTU Audio Express) and a UPS (an APC Back-UPS Pro 1500). I plugged the audio interface and both speakers into the UPS. But it made absolutely no difference -- the whine is still there and just as noticeable as ever. Does anyone know what I'm doing wrong?
My best guess is that the UPS I've got doesn't actually provide clean electricity isolated from my computer. If I pull the plug on the UPS and force it to switch to battery power, it does indeed get rid of the whine, but a) the UPS's fans start up and they are quite loud, and b) the speakers suddenly have a noticeable buzz coming over them that's even louder than the whine. Maybe I've got the wrong sort of UPS?