Motor making grinding noise and burning smell

The cleaner does it's job well. Using on standard short carpet.
The problem so far is after 6-8 uses it started making a grinding noise when pulling backward.
Brushes still spinning just had the noise and the unit still functioned properly.
I only use it about every 3-4 months to clean 3 rooms.
The last use the noise got worse as it was making in forward and reverse motions.
The noise would usually start after using it for 5-10 minutes.
I figured it might be a slipping belt on the beaters and probably water was getting on the belt making it worse.
I removed the circular beater assy by just pulling it out.
Removed the round front beater by removing 3 screws, 2 at each end and one holding the belt guard on towards the middle. Once the beater is loose slide it out through the belt.
The front beater cogs for the belt had some black build up in between several cogs.
I cleaned the cogs very thoroughly, checked the belt for wear and checked the motor gear. They looked ok.
Assembled in reverse, did a quick dry test but didn't fill all the fluids to do a full test. That will have to wait till next time.
Please don't hold me accountable if you try this and break something, the cleaner is made mostly of plastic and the pieces can easily break. Don't try unless you are willing to take the risk, it may void warranty if it gets broken.
If problem still persists then will try using the 6 year warranty that it supposedly has... From what i've read it might be a pain getting it fixed under warranty.
Here are some visuals. http://s1139.photobucket.com/albums/n559/dmayfield1/Hoover/
fell free to contact for questions.