My intake flapper door makes a plastic on plastic noise when I cut the car off and I was wondering what I might be able to do to stop it, sometimes I can here it when I’m driving the car in manual since I shift around 3k sometimes when just cruising

 

You should be able to reproduce the sound by hand when the engine is not running, as the flapper module will lose vacuum pressure and reopen the door.

There should be a strip of adhesive foam on the flapper to prevent such a noise. Does yours have that foam?

 

I unpluged the wire harness from mine and just put it back without snapping it in place. I like the consistent sound of it open for my daily commute. I spend a lot of time between 2700 and 3200 and opening and closing is kinda annoying to me.

I might plug it back in if I take a trip on the highway just in case it improves mileage and reduces drone.