I don't use foil tape on my flexwatt anymore. I used to tape all four sides with the aluminum tape until I had a couple of pieces of flexwatt not heating properly. I was also hearing a constant buzz from the flexwatt. I pulled off the strips that connected one side to the other and the buzzing stopped and they started warming up again. So, I can only assume that the aluminum foil tape was acting as a bridge and the current was flowing through the foil tape rather than the flexwatt. I've since gone to using blue painters tape all around all four sides of the flexwatt and have no issues. No buzzing and every piece of flexwatt is warm and steady...