Tyler....you'll get the same answers here as in the Ball Python section. The white stuff is simply urates, and is perfectly normal. It's really how snakes get rid of a lot of the impurities we get rid of when we humans urinate.
As for the "yelp"....was it out of his mouth, or the other end? I know some of mine can be pretty loud with the "flatulance" that can accompany their feces, and can make some rather disturbing noises in the process...I would be concerned if it actually came from his mouth, but I'd be willing to bet, from the circumstances, that it wasn't.
Hope that helps. And for future reference, it might be nice if you could use a little bit "tamer" term like poop or even crap if you need to be descriptive, instead of the profanity. We do have kids that read here too.