I've noticed this happening many times where the sound and sensitivity setting keep sliding back towards what is perhaps the default position for the item in question.
For example, I initially set the sound at maximum. Then after starting & exiting the game probably a few times, I noticed the slider bar going back down to perhaps 8/10 of the bar only.
The same for the sensitivity bar. I set it at half (middle of the bar). As I play, I noticed the aim gradually becoming slower and sluggish as I go through missions & ops, and when I checked the setting again, it was set back at quarter point of the bar.
As for the music, I turned it off but it does play from time to time whenever I run the app. Had to go to the setting every time at which point it automatically stops when the setting screen pops up.
These items should be fixed in the next update.
iPhone 5 user