drumming noise and loss of control

I have an iMac 27' mid 2011 model and until recently it has been working fine, now quite often, normally when in the email application the mouse pointer starts to flash and move randomly, there is a low bass drumming noise and the menus start to rotate. I completely loose control of the computer and cannot even shut down, even the switch at the back does not work. The only way I can stop it is to unplug from the mains supply for a few mins and then start again.

Has anyone else had this problem or know how to fix it?

What version of OS X are you running? Do you still have AppleCare warranty on this iMac? If it happens often enough, or you know how to make it happen, I'd suggest you take it to the Apple Store and have them look at it and see if they can resolve it for you..

Can't resist! ;P

I read the thread title and immediately decided it was from a Rolling Stones band member who needed a reccomend on some Depends (adult diapers).

Phil27 said:

The only way I can stop it is to unplug from the mains supply for a few mins and then start again.

Click to expand...

That's not good for it. If you didn't purchase the extended Apple Care, I guess it's too late. You have a year from the purchase date. If you do have it, I second the recommendation to take it in for service.