Had banging in room on 2nd floor. ie. pipe banging against joist every time this heat turned off. Had guy bleed all 3 zones and banging is gone! However, every time the heat kicks on in each zone, there is a lot of gurgling & other noises in each heater on each floor??? Each zone has a bleeder above the furnace & there are no individual zones on the heaters. Is the refill valve faulty now for some reason with all this gurgling? Thanks, Ed