Here recently, (one of) the fans have been revving up and down every few seconds, even when the computer is idle. I have had all three of my fans replaced! and it still continues. It's a relatively quiet sound but it's constant and nevertheless distracting because: a. It wasn't doing this for the first couple of months I've had it and b. I'm worried that it's a sign of something going out which might cause further problems later Any ideas?