I have two vents in the back wall of my Tacoma. They are horizontal slots (roughly 12"x1") with a rubber flap inside the slot and a shroud over the slot. I believe these vents are a source of road and exhaust noise. The vents are required for venting air during the closing of doors and HVAC ops. I am considering a flap of material hanging/wrapped loosely over the vent to block the noise out but still allowing airflow through the vent. What will work the best for this? TIA for ideas.