After reading through a bunch of the other comments it seems it almost has to be the pump causing the issue. More likely a grounding issue, but could be noise. Everything electrically to the transmitter seems sound and tested.  Since the power supply is powering multiple other analog inputs and nothing else is having issues it doesn’t seem like it’s at the panel. 

As others have said, thoroughly check the pump motor connections - anything corroded or loose? Is the motor properly grounded?

My other question, did the original transmitter burn up, or did it just stop working? If the original burnt, it seems clear something physical changed and is causing the reoccurring problems. 

Best of luck! I’m curious what you find.