Hi I bought a ball Python on December 3, 09 (approx a month ago) and I'm worried about its health. It's just over two years old and when I bought it, it seemed to be in good health. It ate two days after it was placed in its new home. After about a week of owning it, it started to wheeze/hiss kind of. It started doing it more, and I then purchased a hygrometer to check the humidity. Humidity was at just 25% (I was lead to believe a water bowl in the tank would be enough to keep the humidity up). I upped the humidity to 50% and I have kept it there ever since. She soon stopped wheezing/hissing for the most part, but I still hear it maybe once or twice a day. Its usually pretty quiet and seems to happen when she's working hard. It has now been about 3 and a half weeks since i first started hearing the wheezing/hissing. She still feeds regularly, is active when i take her out of the aquarium,and doesn't really seem any different then when I first had her and she wasn't wheezing.

I know cage setup and environment is a large part of keeping snakes healthy so this is what her setup is like:

15gal tank - 24" X 13" X 13"

aspen substrate (small pieces but not too small, roughly the size of bottle caps)

pool of water (10 inch diameter all around)

hide cave

Heat tape under hide cave

Heat lamp

Humidity is now kept at 50%

Hot side of tank is 88 - 90 degrees, cold side roughly 10 degrees cooler

I've read about respiratory infections and Im really hoping she doesn't have one. If she does is it possible for her to heal on her own?
I'd take her to a vet but I hear they are quite expensive. Let me know what you think.

Thanks for your time!

PS - if you need any more info to help out ask!