Behind dash noise



I have a wonk wonk wonk noise behind the dash just right of the radio and about behind the glove box. It’s getting worse as time goes on. The 1998 Pontiac Montana has about 145,000 miles and still runs good. I believe it might be a louver door on the air handler system. I can’t tell if anything else is under the dash that could make this type of noise. If this is the problem how do I get to the component?