Hello,
Odd problem I've come across. A slot loading iMac has an internal HD that doesn't stop spinning when the computer is shut off. That is, the computer is off and the light is out... but the HD still spins; you can hear the whine. If you kill the power completely (ie. yank the power cord from the socket) it stops. Otherwise it won't.
Any ideas? Could it be an issue with the drive itself? Any suggestions would be great.