digital servos hum... thats a fact of life.. its normal. get over it..
the fact that its not centering right. you obviously messed up the gears during the crash.. go buy a new gear set
install lightly lube them up . and have another great experience until it gets demolished again..
the fact that the servo humms is its constantly trying to center..
every one of my digital servos do it. none of my analog servos do it..
i have around 10 digital servos.. all from hitec