Loud tone from inside Mac Pro

I have a Mac Pro 2.8ghz Mid 2012 system running 20gb or RAM. I have a Phantom drive external eSata, Sans Digital external eSata RAID, a no-name 3 bay eSata RAID and three internal SATA drives in addition to the system drive. What is driving me crazy is a loud and annoying tone that only occurs when I try to unmount drives. I've narrowed the trigger of the tone down to one external SATA drive and one internal SATA drvie. When I try to unmount that triggers the tone. It is very loud and it is coming from the back of the Mac Pro tower. In addition, the one internal and one external drive can not be unmounted when this tone occurs. Even using disk utility gives an error message stating the drives can't be unmounted even when all programs have quit and none are accessing those drives. This problem only began after installing the new Mountain Lion. HELP!!!!! I don't like doing hard shut downs.