check the servo without the pushrod attached to see if there is any buzzing sound.

it doesn't take much to get a noise out of a servo some servos do buzz no matter what, something to consider, moniter your batt. drain, alot of the time the power loss is so little that it is insignificant but noise means that there is something thats not right.

Question; what model.
what servo type.
radio.
what kind/brand of pushrod, and is there guides in the pushrod tubes if there metal rods.
sometimes there can be binding if the guides ar not placed correctly.