[masraum]

Originally Posted by Scott Douglas

Nope, definitely not the HD.
I have a feeling something was doing a check, unbeknownst to me, and it was working the CPU. As soon as I logged off here and went to another site, it quit cycling.
I did open it up and it's pretty clean inside so I let it be.

All seems to be OK now.

Yep, some process probably got stuck. You probably could have pulled up the task manager and checked for high cpu util. I've had some dirty gear, but I've only ever had the noise increase if the fan was going bad (bearings) or the cpu was running causing higher heat and higher fan speeds. Just think of it as being like an alarm.