Yea it's the day the digitals stop humming you have to be worried! LOL
A digi will always have that slight humming noise to it BUT! NOTE BUT! Take one of the servos out or disconnect the control surface completely so you just have the servo horn connected and nothing else. No pushrods nothing. Switch the servo on and listen to the humm it makes. You'll notice it's a rather low volume humm. Now take your hand and apply a very slight pressure to the servo arm and listen to the volume of the humm increase (Stop doing this as soon as possible
). Now you'll know what to listen for when the servo is binding near the ends of the throw range. Avoid binding as far as possible! Now the servos in 3D planes will go through some strain sometimes at full throw as the mechanics of the control setup gets less efficient. We live with this but try to minimize it as much as possible. Think of a car rolling forward...doing what it's supposed to do right? Now put a brick wall in front of it...it's not going to be able to do what it's supposed to and well definitely stop working to a certain degree. You don't want this happening in any servo!