The noise you hear isn't from obstructions, its usually from the air velocity and the compressor. If you could enlarge the duct, it would be much quieter but that would be hard to do. Some manufacturers duct the return air, lessening, compressor noise. Others install decorative panels on the ceiling to mufffel the sound and hide the unit. Fleetwood locates both a/c units forward over the living area, so atleast the bedroom is a bit quieter. The simplest way to get a quiet a/c is to trade up to a $500,000.00 coach. The ones I have seen are pretty quiet.