Also note IDE hard drives have much higher failure rates and are much less tolerant of vibration and heat than SCSI. It's possible a block bolted across the disk like that altered the vibration characteristics enough to throw the heads off. Additionally a lot of IDE disks only have a bearing at one end of the spindle making it relatively easy to put the spindle out of alignment.
Lots of nice data about disk design
here.
Back on HDD cooling, I'm thinking about setting up watercooling for 3 HDDs. I was thinking about a pair of side blocks with the HDDs bolted in and then the bolts mounted on a frame with rubber grommets for vibration isolation. However reading that article has me concerned that the drives would vibrate each other a lot and cause poor performance or errors. Any idea how much more noise I'll get from just securely bolting the blocks to the frame (thus giving the whole assembly a lot more rigidity to reduce vibrations)?