I thought I had a problem with the hard drive on my G5 due to an occasional clicking sound - even when the machine was idle. The sound can happen roughly once every 10 minutes and is a single "hard drive" kind of clicking sound (I think). However, I replaced the drive with a new one and the noise is still there!!! Anyone any idea what this could be? I know that Macs park the heads on drives quite frequently, but surely once parked, they wouldn't need to click again without any activity??