My hard drive makes a grinding sound?

Before mounting and balancing a grinding wheel, the wheel must be sounded. Sounding is loosly suspending the wheel by a bit of twine or other material so that it hangs free, and giving the wheel a very light tap with a hard object. Care must be taken not to damage the wheel when sounding. A wheel that is safe to use will ring clearly and solidly, like a bell or tuning fork. A damaged wheel will not make any resonating sound. Damaged wheels must not be used under any circumstances and are best discarded or returned to the manufacturer. This process is critically important for surface and diameter grinding, where frequent handling, storage, and changing of wheels increases the risk of fatal wheel damage.