Just so we are on the same page on all this: HEAT directs the air out of the register in the center footwell area, VENT directs the air to the forward dash vents, and DEFROST directs it to the windshield dash vents. The additional HVAC settings are labeled AC and cause the AC compressor to be engaged, they can still be used but aren't as effective since the evaporator in the dashboard is also active.
The outlet selector uses a small vacuum network with a bunch of diaphragms attached to a set of flaps; when you move the slider, engine vacuum is directed to the individual diaphragms which then open and/or close the flaps, causing the air to be directed to the selected outlet. The default position (where the system rests when no vacuum is present) is the DEFROST outlet.
First question is if you get *ANY* air from any of the other vents, or if you only get heat from the three available settings.
If the DEFROST position is the only one that works at all, then you probably have a vacuum leak. Pretty common problem and it's been covered here many times. There is small vacuum reservoir behind the front bumper that gets cracked or deleted with off-road use, and that's probably the source of your problem. Also check the plastic and rubber hoses and tubing and make sure everything is connected
It's also possible that you have a problem in the dashboard itself. I had a small leak where the vacuum manifold is connected to the HVAC controller, and had to clean and seal that for things to work again. The noise you hear might also indicate a broken flap somewhere.
