If there is a potential difference between the power supply ground in the field device and the (-) return on the AI, then the signal will have an 'offset' created by a ground loop caused by the difference in ground potentials. The offset will affect all the AI's, not just the one causing the ground loop.
This happens quite commonly with single ended AI's. If it happens, then you need a signal isolator (4-20mA input/4-20mA output) to get rid of the ground loop.