intermittent gpr buzz replaced gpr didnt help

[scpbmxer01]

I am throwing codes p0670 and p0683. I can hear my gpr buzz randomly on start up I replaced my gpr and tested the system following nchornet's directions and everything checked out good I dont know where to start. I can clear the code and it pops back up about 30 seconds later. I have been reading a lot how do I trace the problem back to the pmc? is there a harness i can buy?