My A/C venting systems CLICKS like someone knocking on a door. on 2005 Nissan Titan

I think it's a valve gate on the ac vent trying to open but slipping, any idears?
It's intermittent also.

Asked by for the 2005 Nissan Titan
yes you have an a/c blend door with stripped diag on which one or try to find it yourself and repl as required