BF-109 combat flaps
 

Can anyone tell me how to turn off the combat flap beeping noise? Can I change change it in a sound file or somewhere?

Lower your gear or raise your flaps.
It's the only way.

You should only use flaps for very short periods of time anyway.
don't let the name "combat flaps" fool you into thinking that you should have them down in combat.

The drag they cause will mean that you will always be slower and climb more poorly than an equal opponent.