1993 Suburban knocking noise

Hi  I  have a  1993  suburban and  After I
start it I hear a tapping or knocking noise  coming from the up
front passenger side of the  truck by the glove compartment. It
stays on for about a minute or so after I start it and after I turn the
car off.  I was wondering if anyone knew what this could be? I
thougt it might have something to do with the AC. Thanks for your
time!!! -Johnj< ="">

I have the same problem.  Its a little flapper valve located on the far right bottom corner of the heater box.  Its some type of fresh air or recirculation flapper.  If you will notice you can move your controls from different settings and it will make it flap doing that.  I have put up with it for about 2 years and wish I knew the fix.  Let me know if you do.

Shayne7s38695.5911226852