Why does my Saxophone Squeak?

I've been playing for 4 years in band and now I'm in the 9th grade band. On Friday, I have an audition for Wind ensemble and as I'm practicing I hear squeaks, and can't seem to blow much air through. I've tried fixing my reed multiple times, Nothing seems to work. My saxophone is a Selmer Bundy and seems pretty old. I bought it from someone and It have a lot of scratches and a small dent on the bottom. The padding is also poorly done and all this will be fixed next week after my audition. What can I do to stop the squeaking?