Okay, this is going to be a very non-technical question ... so please bear with me. We have a hydro-air system, a Peerless Furnace and First Co (air return??). Our house is 1.5 yrs old. Recently, we've had a clunking noise reverberating from the basement which I have found to be in exact 6 hour intervals. What happens is one of the zones (we have 3) calls for heat, the furnace turns on, about 2 minutes later the furnace turns off with a whoosh and then across the room by the air handler there's a clunk. I've had our furnace repair guy here and he's disconnected the wires to the furnace from that zone and the noise doesn't happen. Then he tried disconnecting just from the thermostat and it still happens. He thinks there could be a crossed wire? But it doesn't make sense that something is timing this at exact 6 hour intervals. Any ideas, this is driving us crazy!!!!