One of my fans was making weird noise the whole weekend. Now when I finally proceed to open up the case and try to fix it I noticed it's gone, very disturbing.. It was sort of like something touching the fan blades very gently (like a piece of cloth or something soft) and it would last for 1-2sec then stop for a brief moment and continue again, was driving me nuts.
I should probably open it up anyway for dusting and such but I've gotten lazy after I moved it under my desk. Need to remove all the cables and lift at a weird angle to get it out. Maybe I could remove the front panel and stuff a leaf blower in there...