You can have the unit serviced by filling out this service request. Unfortunately, I don't know what the problem could be based on the description, but it's best to have your unit inspected and repaired.
I have an HT-Z510 Samsung unit that makes a grinding noise after being on a few minutes. The only way to make it stop is to turn the unit on and off a few times. I suspect the noise is somehow coming for the DVD changer? I have no way of knowing. I'd like to get this fixed.