Since you do not have a MIFM yet I would try swapping the ESI cards and make sure the issue does not follow the card. Next I would either try a new tail or swap the tails and test to make sure it is not a bad tail on the system. Lastly I would back the system up then default the system and see if the issue exist when the system is default, If it does not work when the system has been defaulted and everything else tested you have a bad back plane to your system.

Good Luck