Originally Posted by Billy T.

Ok, we have a little more information to work with. All three servos that you mention are analog servos, so the noise you are hearing would be more of a growling noise than a digital buzz. Analog servos will only ever growl when there is a constant load on the servo. You will want to remove the horn from the servo and check the steering linkage on your truck and make sure that it is free from binding. Keep in mind, that because the vehicle is a crawler, there will be a load on the servo while driving, so expect some noise, and a little bit of heat build up due to the load and the fact that there is very little air flow on the servo.