This is the same issue I've been having, though it started as an occasional noise and is now going almost steadily.. And yes, sometimes I think it will last off too! Sonds like gardening equipent!
I also wondered about cleaning it as mine has been getting worse and I use it regularly. Since my laptop is over a year old and out of warranty I may just open it up to see what I can do.. maybe find a replacement fan that is quieter?
