Thanks. I sure would never have considered this. Interestingly, both TV and Router plug into the same UPS.Maybe the TV (and test switch) AC power supply ground/neutral is not properly bonded to the router's AC power supply ground/neutral (a building wiring issue?)... when testing, is all of this equipment using the same AC power outlet? If not, try powering the router and the TV from the same AC power outlet so that they have that common ground/neutral and no voltage difference/ground loop current between their chassis. Admittedly, a long shot guess but one must think outside the box when troubleshooting the unknown!
OE