Guess I've had enough problems with HH to learn most of the noises: first, the motor starts for about 30 seconds (prime), then the burner fires (easily heard), then when the burner stops, there's about a minute or more of cool down of the motor running.
I find that when it is real cold and the furnace is on by the thermostat, that it cycles on about every 5-10 minutes during the night - on for a period then off and back on again 5-10 minutes later. I usually sleep through most of the cycles. I assume that this is the temp in the tank going down as it pumps fluid through the system and the tank's sensor turning the furnace back on again.
The HH compartment is located on driver's side, just forward of the rear bedroom slide, just aft of the utility compartment. the exhaust is right in front of the left rear tire.
David Horn, TX; 2014 40ft Phaeton QTH; 2014 Mazda CX5; 2013 Can-AM Spyder RT-S on TandemTow trailer; Traveling with Ringo (an English Cocker)