I have clicking in what appears to be the gas line whenever the furnace kicks on. I have heat, the clicking is loudest near the gas line on the water heater, but I can hear it upstairs as well. When the furnace goes off, the clicking stops. Does this sound like a furnace issue or gas company, don't know who to call, can't afford "extra" trips, but don't want to blow up either! Thanks for any input you have