Post probably to old to find in search but several (not challengers) experimented with baffles covered with soudproofing material in the return air path. Actual db levels measured before and after did show modest improvement. Not much you can do about sound coming out of the vents without restricting air flow which is a no-no.
Suzie & Chuck USNR USAF USCGA Challenger Owners Club 2015 37KT Challenger, Demco Commander tow bar, Ready Brake, Sewer Solutions, Safe-T-Plus 41-230, 5-Star tune, towing 2017 Ford Edge FWD 3.6L V-6 four down & 385 FastTrack kayak in the basement.
Summer - Creede, CO Winter - Okeechobee, FL