The number seems excessive unless you are pushing oodles of amps through a fancy games machine, but which if any are not really necessary, is a different branch of your problem.
Simple things first.
You have obviously cleaned everything thoroughly and looked for odd screws rattling about inside the case, or any bit of loose material rattling in resonance.
Worn or dry bearings is a more likely cause, particularly if you have a chattering noise, groan or slight squeal
Identifying which fan is sometimes easily done, but you will have to leave the case open until you hear the noise.
Then using a soft brush or a paper spill briefly stall each fan in turn until the culprit is found.
Once found, replace it, any attempt at lubricating it is a short term remedy