If some driver was involved in the situation, and I do not know if it is, you could try running
Driver Verifier. Check the link and make sure you know how to turn it off using the /reset switch.
Running the basic
Verifier /all will check all your drivers. You can check just one if you desire. The link has links to pages for using the command but other web sites also contain directions is using the Driver Verifier.
Driver Verifier (Windows Drivers)
You need to know the
Verifier /reset will turn off the checking in case your system Bluescreens and you need to start in Safe Mode and use the command prompt to turn Verifier off.
The fact several systems are doing the same thing would make you think they had something in common. Maybe an external device or networked device is being accessed. If a virus is involved they may have the same one. Having multiple hard drive failures at the same time would
not seem to be likely.
Have you tried moving one of the units to a different power supply and/or disconnecting them from the network?
But if you have done a clean install of Windows and the problem reoccurs, there must be a hardware problem, some common software you are running, or something else not related to Windows 7.
You did not respond in regard to the system running normally in Safe Mode...