Just brought my 05 Newmar Kountry Starhome today. While getting used to it and having the heat come on there is a considerable amount of fan noise being generated from under the refer where the heate...
Read installation manual for your furnace, determine how large the intake screen must be and reduce the intake screen by blocking all but what is needed. Line the area where the furnace is installed with sound deadening material from car stereo shop.
I did this plus a few other mods and reduced the noise by 50%.
The vent opening on mine was twice the size the manufacturer required.