60 HZ Hum on Analog Input PXI-6229

Ther is a 600mV common mode noise hum being introduced somewhere on the circuit below. It is causing the PXI-6229 to read inaacurate measurements. Is there a way to configure the device to reject common mode noise? Or any other suggestions?

Is the metal box connected to both the power system (safety) ground and the signal ground? This could be the source of the ground loop. Are the computer, PXI chasis, and the metal box power all connected to the same branch circuit and ground?
Try drawing a diagram showing every ground connection in the system.  Do not just use a ground symbol but actaully make it a wiring diagram which shows where every wire, chassis, box, conduit, or anything else grounded is connected. This can sometimes be useful in discovering ground loops.  I found one which included a wire attached to the mounting bolt for a toroidal transformer. It resulted in several amperes flowing through the housing of a very sensitive magnetic instrument!
As has been mentioned CMRR only applies to differential inputs. The circuit you posted is single ended so I think it is unlikely that a differential connection would help.  
Lynn

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