A few weeks ago, my furnace blower got quite loud. So I removed the access panel to see what I could see. The fan blades were caked with dust... so I figured it was just out of balance. Pulled the squirell wheel, and cleaned most of the dust off. This just made it worse. Cleaned it a little more, and now it shakes so much, it sounds like it is banging against the side of the box. Any clue?