I have something of an odd issue. About two hours ago my Rev C 12" PB started humming. It's this faint, high-pitched soft whine. Tilting the chassis would slow the hum until the PB came to rest. The machine then froze up slowly and eventually became inoperable. I rebooted, waited a bit. PB booted fine, worked fine for 5 minutes. Then I heard faint "pings" at odd intervals and the humming sounds soon after. Then the PB again crashed. It seems to be working fine now but I'm still hearing a faint humming.
There is no distinctive clicking or scratching as is usual with a HD failure and both DiskUtility SMART status and SMARTReporter are giving me green indicators. Any thoughts what it could be? I've backed up everything just in case.