propane heater start-up noise

I have a 2005 2720 and the propane heater recently started making an unusual noise for a minute or so at start-up. The heater still functions and puts out hot air. The thermostat seems to work fine. The noise is sort of a chugging sound at 3 or 4 pulses a second and fades away after a bit, but is kind of loud. It does not sound like a high frequency tapping noise like a fan hitting something. I am concerned that this may lead to some kind of heater failure.
Has anyone noticed this before and resolved it as a problem or not?
thanks,
Mike

Can't think what could make the kind of noise you describe, except a fan.

There are two fans within the furnace enclosure. One is a conventional fan-blade fan; the other is a squirrel-cage fan. The squirrel cage especially could be rubbing against something until it comes fully up to speed. Either one could swipe past something, especially if it is a bit out of balance. When the furnace starts, does the chugging slowly increase in speed, or does it start at full speed and maintain that speed?

Or there could be a dust bunny or wasp nest caught in either fan.

The silver air inlet-outlet panel is mounted on the outside of the front wall of the lower box. You might pull it off and look inside, to make sure there is no trash or blockage. Wasps and other critters like to get in there and build homes.

Bill

Thanks for your reply Bill. I dropped off the trailer to my local Trailmanor dealer Scott at CustomRV in LA and he confirmed the noise - said it was unusual. He removed the unit from the trailer and dissassembled it and did not find any obvious rubbing but did find a wire connector that was loose. He put it all back together and the noise is gone! He also found a problem with the thermostat and replaced that. So all good now - seems like an electrical bug rather than mechanical.
Time for our road trip!
Mike

Good stuff! Scott at Custom RV is the best. You did well to find him.

Bill