Last month we had a Lennox G26 (75,000) installed. So far so good, except for the clunking when the gas valve opens and closes. This sound resonates from the gas pipe to the floor, I guess. It's not a big problem, but our 23 yr old Carrier didn't do this. The rest of the furnace is alot quiter than the old unit. The dealer said it's a new (dual or double) gas valve design. Is this correct? Should this be happening?