A digital whine is normal. Hitechs really do this. Also many servos will chatter when you are using a 5-cell pack and the voltage is really high. It's nothing to worry about, although your buddies will think there is. 5-cell packs can get up to 7.2v. A voltage regulator like one from Maxx Products (<$20) will cut it down to 6v and eliminate the chatter.