As many of you will probably notice in the days ahead, we've just added background music and sound effects to the game. You can enable or disable music & SFX independently on your Settings page.
If your browser supports local storage (all modern browsers do) then the game will also make sure that background music only plays in one tab, no matter how many tabs of the site you open.
We welcome any feedback or bug reports here on the new feature. But please, before reporting any issues try doing a "hard refresh" on the site (CTRL+F5), this will clear out cached data such as out of date javascript.