Check out this YouTube Video:
After reading a ton of forums I thought I needed to replace the clutch assembly. My Dyson was making a horrible noise when in "carpet" mode. Got a new clutch on eBay for a great price. Somewhat hard to replace, but thanks to the YouTube video, I was able to get it in.
HOWEVER this did not resolve the issue. I realized the beater bar was not spinning or was slipping. I thought I cleaned it all out but realized you need to take the beater bar out and pop the end cap out and clean the INSIDE of the beater bar. I additionally sprayed WD40 in there.
It spins great now and in the end I think that's all I had to do was clean out the cat hair build up inside the beater bar. But now I have a new clutch & belts too. Hopefully won't have issues anytime soon.