<strong>Yahoo Message Number: 3578</strong>When my Webasto furnace is running I get a lot of knocking sounds from the vicinity of the hot water tank. I don't hear it when the furnace is not running. It sounds like a water heater when it is getting limed up and knocks whem steam forms inside the tank. I don't know why it would only do it with the furnace heating the water. I've drained...