The build up of saw dust on the exit side? Both of mine have spots with build up on the exit end. Or little spots around the control panel that have air leaks that have build up. I also, on my older unit, have dust trapped behind the clear plastic that covers the speed/timer lights.

Guess I shouldn't be surprised for something only costs $125. Also shouldn't be surprised when the bag filter has a 1/4 gap at the top between the filter and case that they try to stop infiltration with a cheap foam gasket.

EDIT: Just noticed that my new one 3.5 months old has dust trapped behind one of the light covers.