Hard Disk drive failures...or not.

A friends pc came back for diagnostics/repair after claims that the boot device was inaccessible. When I booted it up this afternoon it worked fine for about 10 minutes before crashing with a Kernel error. MS lookups showed this was an error in the SCSI plane or devices using the same interrupts. There were no SCSI devices in this box. The disk was making some nasty clunking noises though. Popped it in the other machine and ran a quick test on the disk and it failed with a Read Test Element and told me that the warrenty had run out on the 22nd Feb this year! I backed up the data using Ghost and then ran scandisk which gave no errors. Popped the disk back in the original machine and ran a quick test followed by a full test - no errors (and its nice and quiet again). I guess the first test relocated the duff sectors..
Hopefully the disk will last a bit longer now and at least it now has a backup of the machine, the latest antivirus updates (not a year old - tut tut tut!) and all the windows patches installed.
Shouldn't have spoken so soon...first boot into windows and the clunking starts up again and the machine hangs when I try to install the AV software :-(
Update Ok - it was the disk even though there are no errors reported by the software. I replaced the disk with an old 6gb drive and everything seems to be hunky dory. Now downloading the 42mb of patches for windows.