Scratch

Ok, so I'm making a game (similar to the very first Legend of Zelda) and when the character changes screens, I'd like there to be musical changes, too.  So, when he goes from screen 2 to screen 3, I want a different track for 2 and for 3.  How do I cause the other music to stop?  I can only think of extending the tracks so long, the music can't run out.  I "change screens" by having the character, when he touches the end of screen gate sprite, broadcasts whatever, and the rest of the sprites that appear on that screen disappear, and the ones that are on the next screen appear.  Then, the main character is sent to the opposite edge of the screen, and the background changes.  Anybody have any experience with this, and can they help?  It would be much appreciated.