Scott17, that didn't work out for me. I opened the four big main screws, opened the two small screws holding the motherboard, took the two screws holding the fan. Tried assembling again many times, with all screws loose. Still buzzing. I ran it with just the motherboard on table and fan hanging out and then I noticed that if I actually push the silver sticker part (just very slightly), the noise goes away. So then I got some Blu-Tack to give pressure to that sticker part. Assembled again, but it didn't help at all (after disassembly I could see that Blu-Tack was flattened so it did play a part but didn't help).
So I gave up with that. I would still have warranty left, but I don't want to wait for another ~4 weeks for the shipping process. So I am wondering whether a new fan would help (at least it should be easy to install if it's the same size). I found: http://www.ebay.com/sch/i.html?_odkw=bsb05505HP&_sop=15&_from=R40%7CR40&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.X%22bsb05505HP%22&_nkw=%22bsb05505HP%22&_sacat=0
Has anyone tried to exchange the fan (where did you buy it from if you did)?