I found out the problem which I think it's a bug @AShley please shed some light.
After excruciating tests
I found out the following.
The music gets started BEFORE any other sound (the song is in the music folder). Sound do NOT get loaded until the song finishes to stream. This is the reason why the title song (which is only 20 seconds long) do not create this behaviour. I'm using the latest (stable) chrome.
I fixed this by moving the music in the sounds folder, but it's hackish since this way people will have to wait until the song streamed before hearing it.
Solutions (apart from preloading)?