Heat/ A/C Vents on 1997 camaro not working...

I turn my switch to the front vents and the air will not come out the vents, instead the air will blow out the defrost vent and the floor vents, its like something is blocking it. This first happened when i got the car a year and a half ago. Then one day the front vents started working..... for a good year or so, until about a week ago and they don't blow any air anymore once again. The switch that control the intensity of the air works fine, and the temp switch work fine, and when i use the switch to just have the defrost on, that works. I also noticed a faint blowing of air sound coming from behind the glove box.... this just happened recently after i installed my new radio deck. Any ideas about why the front vents don't blow air and why that blowing noise started? It makes the blowing noise even when i have the air off. thanks.

You have a vacuum leak somewhere in the hvac control system. The defalt is the defroster vent. I would start in the engine compartment and work back toward the control in the dash. Shoebox's site has some pictures of the vacuum canister on his web site. Here is one but there are others there too.
http://shbox.com/1/vac_check_valve.jpg

what do you mean by the default is the defrost vent??? Is this an easy problem to fix without taking a bunch of crap apart??? How much would a repair shop charge you to fix this???

My site also has a diagnostic (http://shbox.com/1/4th_gen_tech2.html#HVAC_vacuum)for this common problem.