well, I repaired the "Pro" model today. and yeah, getting it back together was a major challenge! I believe the entire issue was that waxy brown stuff that collects on the "Blades" also collects inside the unit. I found a lot of it in a hard to reach area, mostly on the white insulators where the wire connects on each end. Once cleaned, all set. Yes, they do buzz, I think that's normal, especially in a dirty area. I had mine for ten years and this was the first real cleaning I had to do. You can put all the screws back if you want, I didn't. it's working very good again, but I lost the red LED, or clean light. don't know what happened, but I had mine completely apart and didn't think I would be able to reassemble it. The swing out filter part was the most difficult to reassemble, but, it was easier than it looked. wish I took pict's. It's about an 8 out of ten on the skill level . Good luck.