Thank you for helping.
I checked the input offset and indeed, I was getting 0.
I also checked for the ground loop, but I was getting the same offset so there is no ground loop.
I was using before the USB-205 single-ended DAQ and the offset was 0.04V so I moved to a differential DAQ in order to reduce this offset and it got reduced to 0.02V. Is there anything else I can do to get rid of this noise? I thought that changing the DAQ to a differential model will reduce the noisy in a more significant way.