Ifyou have the drive out, it may well be worth checking the 20GB drives are mounted on standoffs (well, washers). These drives have a tendency to misbehave if screwed down to the cradle - not all do, but some do.

I think Tony did a faq entry on this, but basically it involves putting M3 washers between the drive and the cradle on each screw. This relieves the pressure on the drive's spindle, which on the IBM 20GB is much closer to the bottom of the drive than other drives - the 20GB is the only one we've seen this problem on.

Hugo