[Shotimes] Flap, flap, flap noise in the dash

[Alan Fanning]

OK, no sooner do I get our "new" '95 ATX on the road after a lengthy wait to
fix a rear control arm issue then we find that what is presumably the blend
door (?) is going flap, flap, flap behind the mid-dash area. It seems to be
intermittent but it's the wife's car and I haven't actually driven it but
once since this started.

A reminder as to the cause and fix for this problem would be appreciated.

    Alan