Overview:
When entering the submenu for a specific stage (e.g. Rusty Ruin Act 1), pressing the back button to return to the stage select menu will restart the music.
Steps to replicate:
1) Select a stage that has already been beaten once.
2) Select the back option on the submenu.
3) Listen, as the music has now restarted.
Additional information:
Performing the steps above produces another (potentially) unintended effect: Sonic will always replay his arms-crossing animation and will default to facing towards the right (even if he was facing the left when the submenu was entered). My slightly educated guess is that exiting the stage submenu causes the entire stage select menu to be "restarted" using only information about which stage's submenu was exited out of. Not sure if VRAM has enough space to avoid needing to reinitialize the entire level select menu, but if not then placing hooks for the current position in the song track (and possibly the direction Sonic is facing) would be suggested.
If it's left to run, it slows down when decompressing data. It sounds better restarting in this instance