AC Trouble

[lebolewis]

This one has got me stumpted! There is a tapping noise coming from inside the AC/Heater enclosure, over on the passenger side, just above the foot area. The AC/heater seems to be working OK. This is on a 1994, GMC, Suburban, 2500 series.

 

It starts tapping instantly after I turn on the ignition and lasts for 20 seconds.....and then it stops! It also starts tapping again when I turn the ignition OFF, and last for 20 seconds! While it is tapping, if I press the MAX (recirculate) button on the AC, it stops for about 5 seconds and starts over again and last for 20 seconds!

 

The tapping noise sounds like it could be a baffle door rapidly clapping closed, open, close, open, close, etc. The part that really stumps me is that it does this when I turn the ignition OFF!!

 

Help!!