The brakes are only supposed to stop the truck and cant hold the truck in place on a hill or anything. Be carefull not to set the brakes too high on the ESC or it WILL endo! The noise you are hearing is perfectly normal.
^ Yes! Additionally that noise is a combination of the big electric motor and the large toothed steel gears clashing together. That sound tripped me out when I first got my truck.
Also, regarding the braking power, as CR500rider stated too much brake is probably worse than where it's set right now. If you hit brakes in mid jump, the truck will spin into a forward flip. Looks cool at first until it lands on it's lid; then it's not so cool when you have a smashed body.