when a minecart activates, the sound will play after it has stopped, pressing esc will stop the sound but minimizing then opening up minecraft again will make the sound play again, this can only be totally stopped if you exit out of that world.
How to reproduce
1. open minecraft and a world
2. place down tracks (about 4 or 5)
3. place a minecart and push it, the sound will continue after the cart stops
4. press esc, then back to game, sound will stop
5. minimize minecraft
6. open it again and click back to game, sound will continue