So this only seems to have started today. Every 5-10 seconds I hear my PC -- pretty sure it's a cooling fan -- make a "revving up" type of sound, then it dies down, then a few seconds later it does it again. It's been doing it all day and it worries me. I restarted, but it still does it. Is there anything that might be causing this that I can fix, like a software issue perhaps? It hasn't done this before.