Double cab rear cabin vent rattling

I just installed 2, 8 inch subs via oem audio plus, as well as sound deadening and ensolite on the rear wall. The issue that I'm running into is that the black exhaust flaps are being rattled, which makes an obnoxious sound on the outside. What has been the solution that most people have used ? I don't think covering the vents is an option. There would be cabin pressure and the interior would always feel stuffy. Thanks for the responses.

 

I just had a Jl stealth box installed and having the same problem I can hear it inside as well