Beeping on Dell Poweredge Server (RAID Fault)

I like running old hardware as long as possible, but I'd get the machine replaced. You're going to have a tough time making any headway in resolving this issue.

My suspicion would be subtle interaction between the firmware on the "failing" drives, possibly the hot-swap backplane, and the RAID controller. No one at either Dell or Fujitsu is testing those drives what that controller anymore, and you're unlikely to get anyone at either company interested.

You're puting the array at risk each time this happens, since the array is becoming degraded and being rebuilt. If a legitimate failure happens on another disk during the rebuild process you're going to be in an array failure scenario. Hopefully you've got good backups.

It's frustrating because adding disks really should work fine, but with something this age you're really better off biting the bullet and getting something with active manufacturer support.

Does the server have a RAID controller (PERC)? If not, you won't be able to configure RAID at the hardware level, you'll have to configure RAID at the software level in the Windows disk management mmc.