Have you tried re-seating the power/data cables into the MB & drive? I had a similar problem about 2 months ago in that one of the secondary drives would make a 'clunk..tick' occasionally, as though powering down. Note that 'clunking' in hard drives is usually is the sound of the heads parking suddenly. The drive would be removed from the list of available drives in windows and would not be recognised on re-boot.
Removing the PC cover & re-seating the cables has stopped this occuring. It is possible for connectors to work loose due only to thermal expansion/contraction as the PC is powered up/down.
Last edited by Bo Nalls; 26th December 2006 at 16:27.