Comment: Cleaning and greasing (Score 1) 4
I had this problem with a heatsink fan a while back.
Though I ultimately had to replace said fan, I found a solution that worked at least for a while. I disassembled the fan and took a green kitchen scrubber pad to the shaft of the fan, to remove stuff that had essentially cooked onto it - dust particles, hair and whatever else got into the case. You'll be able to feel that stuff on there even if you cannot see it. Steel wool is not good as it can scratch the shaft which will make the problem worse. Once I had it smooth and clean, I took just a small amount of axle grease and applied it to the shaft with a toothpick. I was careful to make sure I wasn't heavy-handed with the stuff but I made sure there was enough to coat the shaft and that it still turned easily. Then I reassembled the fan and all was well for a while.
This did not fix the problem permanently. Eventually the fan got loud again and I redid the procedure several times until I replaced it outright, but it did solve the immediate issue.
Hope that helps.