[woodman]

We had a similar problem. Had to remove basement walls to access, but discovered that the aluminum duct hose had come loose from the ductwork. I fabricated a plenum, out of aluminum sheet metal, then secured it with some rigid metal straps anchored to the the aluminum floor joists. Labor intensive and difficult to access, but now it's better built and permanent. Given the constant bouncing you get while traveling, the system was designed and built to fail. It's not just Montana's either, there are plenty other companies that build with speed and not integrity.