>Get a can of compressed air
>open 'er up
>spray the fan and stuff with it (don't hold it upside down or in a position where liquid in the can could leak if it were an open-top cup, because most compressed air cans use liquid nitrogen or something)
might work
If you do anything wrong i'm not responsible
edit: also this is from personal experience, but if it's really loud there may be another problem
does it sound like a car with a bad motor but quieter, or like stuff is colliding?