If you're hearing it at night, when it's quiet. the easiest way to determine if it's the water heater is to turn it off in the early evening as soon as you're finished using hot water, then when you go to bed, it should be "somewhat cooled". If it doesn't "gurgle through the night" it probably was the water heater, if you still hear the "gurgling", get with Tom (Crazy Cain) and see if his "spirits are still drinking his spirits" or if they've moved on... If they're no longer in his trailer, you may have "un-invited guests"