We had problems with no air flow to the heater vent in the bedroom. Rockwood guys dropper the bottom, opened up the duct and found -
A Giant Mouse Nest!! made up of shredded paper towels.
Must have happened the first winter, I had found a similar nest under the kitchen sink and under the drawer in the bedroom dresser,
What did they find your problem was?
Rick & Debbie; Brandy & Schnoodle Dexter & Fritz R.I.P. the Doxie "Kids"
2015 Jayco Pinnacle 36RSQS 5'er
2013 Chevy Silverado 3500HD LTZ, 6.6L Diesel Dually; B&W Goose Neck and Companion 5'er hitch