I have a strange noise coming from the rear deck area in front of the back window. With a window open or the HVAC set on RECIRC, I hear a strange flapping noise over rough surfaces. If I close the windows or turn off the RECIRC feature, it goes away. I see that there are two "flapper " vents on either side of the fuel tank. Anyone know anything about these vents and their function? Many thanks...

 

They are the cabin air vents, that pass air into the boot, then it works its way out from more vents under the rear bumper side skirts.

Originally had foam coating to prevent such noise. So age has taken that foam to a resting place, and left the noise behind.

Not sure of the fix ease, maybe the tank out, or maybe the seat back out MAY give access, dunno.