Hi Dave:
We had the same situation:
we were trying to figure what changed -- computerization of our office, LASERS from those printers, high tension wires running a mile away etc..
turns out it was the sticky pads- we got a bad batch. We changed our vendor to cardiologyshop.com, that worked for us.
long ago we had to replace the cables, that had worked too.
I would suggest changing the sticky electrodes on body. that is the least expensive start...
good luck.
