Music isn't fully done/implemented. Or rather, the music that is done isn't for the set of levels currently available.
The hit sound effects I kind of agree with, but I'm waiting until after music is done to do more with sound effects.
And the sprite appearing on screen when levels load in is because it's a placeholder for animated loading screens (gotta make sure the animation itself is working and all that). I keep forgetting to warn people about that... but yeah - thank you for playing and rest assure that's not a bug.