Volume level setting on my tv.

What's going on with my volume level control?

Recently I have noticed a problem with the volume level adjustment on my xfinity remote. Usually I listen to the volume on level 10. The other night while watching a movie on TV I pressed and released the volume button to change the volume level 11. The level went from level 10 to level 12, which was way too loud. I could not change the volume to level 11. I tried to go to level 11 several times but the level changed to either 10 or 12. I unpluged the box for 30 seconds and after rebooting I still had problems adjusting the volume level.