Dell R720 - can't install any operating system
I would check that the firmware across the board has been updated to the latest versions (BIOS, PERC, disks, etc.) in case there is an issue that has been resolved already.
If the issue continues I would replace the PERC card and get one with the battery if possible (you really don't want corrupted disks in the event of a power loss and it'll allow you to use write back caching safely which will improve write throughput to the array).
If it still persists then look at the backplane itself. I've never experienced a backplane problem, but it can happen.