During our first trip out in our new Bighorn 3400RL it got down to 34 degrees at night. We used the heater and after 5 minutes or so we heard a popping noise from the ducting near the heater (sounded like metal ducting). Just one “pop” and then it was quiet. A few minutes later it happened again, this time from the middle of the rig, and then after a few more minutes again at the rear of the trailer. After the heater cycled to the off position, we again heard the “pops” this time in reverse order. They were loud “pops”, enough to get our attention…and bothersome…anybody have any ideas?