If so, check with your Apple Store. It may have a bad HD like mine. I also found a weird problem that was in the SuperDrive conroller. It was also taking over the HD. Whne the CD spinms up, it also spins the hard drive, too hard. My super drive is much quieter after a HD replace.
My point is:
IF YOUR IMAC IS NOISY, BRING IT IN!!
My point is:
IF YOUR IMAC IS NOISY, BRING IT IN!!