It really could be anything... Test any extension cords and power strips you have as well. I had a power strip go bad on my 240, and it was causing everything that was plugged into it to leak voltage. Once I replaced the power strip, it was fine. Also, look for salt creep on the prongs of everything. Clean them off if you find salt creep, and replace any plugs that are corroded. It's important to keep everything as dry and away from the salt as possible. I had a stray voltage in my 90 a couple months ago. My grounding rod had gone bad and wasn't working anymore.