2016 F-150 XL has a noise in the heater system only on the "floor" setting, going down the road. Goes away with recirculate, off, or any position other than floor. Sounds like paper or cellophane rattling in the plenum. Just started. 18000 miles. Drives me nuts. Anyone else have this problem or ideas.

 

If the truck is still under warranty, I'd take it in.

 

Yes, it's under warranty, but I would like to investigate the noise & try to fix it myself instead of having someone disassemble the dash and plenum and toss the left over screws and parts.