No, that's either the fans starting up or the disk drive booting up, or both. In my case the humming NEVER stops, even when powered off.
I just unplugged it 30 minutes ago and the humming stopped when I plugged it back in. About ten minutes later, I turned it on for five minutes and then turned it off and left it for ten minutes, when I came back it was humming again.
I saw on CAG that next week BBY is going to have a deal where if you trade in a ps3, you'll get $50 off a new ps3 bundle, so I'd get a new console for $135 off. Not that I have the extra cash though....
Are there any known issues with the super slims?
Yours sounds like the power supply has bad resistors which mean it is going to stop turning on someday..