Grounding cDAQ-9171

[BroJA]

I am trying to set-up a National Instruments cDAQ-9171 with a NI-9231 input module with very limited luck, as large 50Hz harmonics are present due to mains interference being present. I was hoping someone could point me in the right direction in terms of grounding methods. Am I able to ground the cDAQ-9171 chassis to a 12V battery (car/motorcycle/NBN) with the added benefit of powering two pressure transducers, thus avoiding mains interference? Or do I need to go down the track of connecting to the "grounding electrode system" of my home. If there are any other recommendations, please let me know.

Currently the test set up consist of:
2 x MRH21 pressure transmitters
1 x cDAQ 9171 and NI-9231
1 x 24V desktop power supply (bare wire)
2 x microdot to BNC male (with BNC female screw terminals - removing soon as I am hoping this is the cause of my issues)

For additional information, I'll attach the Matlab script, frequency/time plot and pressure transmitters specs I am using for my application if it helps, cheers.