Heater Electrocution HELP please

So I had 2 Rena smart heaters in my tank, I noticed they weren't heating so well the temp would rise and fall and rise and fall. then I noticed I got a very mild tingle from them but only in the sump. at first I thought it was because I had a cut but after checking on it became unmistakable. Seemed to happen with both heaters. So I took a JBJ trutemp from another shutdown. Plugged it in it was fine for a little then started getting a mild shock again. at this point im convinced it is the power bar so I plug the heater into a completely separate socket and I got a BIG jolt this time. (if I touch the glass and it has a little water on it I can feel a tingle) When I unplug the heaters there is no shock whatsoever. obviously instinct leads me to believe there is something else wrong here, or I could be unlucky as all hell and all 4 heaters I tried are pooched.

any thoughts?