Yeah. Garage dust just sticks different. No idea why. My guess is because the car goes in and out, but maybe also because it's a non-heated Australian shed sorta number ...
As opposed to what, Canadian heated sheds? Also, Racist. ;)
I reckon it's all in your mind but also it could be a higher quantity of exhaust gases and car brake dust. It could be overspray from other stuff you do in the shed (if you're a WD40 fan, for example).
Dust? You MTB right? Dust shouldn't make them squeal. Blow them (lucky wheels) instead of wiping.
FYI: isopropyl alcohol in bulk is cheaper than the sprays if you're not already using that.
Another option is to run metallic pads all the time anyway. They already squeal so you just get used to the Built-in Pedestrian Warning System™