To answer ur question.....Digital servo's have a WAY more accurate center line on the Pot..therefor they are ALWAYS trying to recenter.....causing the whine ur hearing.....analoge's are a little sloppy around center and dont mind as much.....its no big deal with a little load on em....but as u said there whining at idle...with No horns on....thats not right....they should be Dead Silent....I would look into the top case of the servo and see if u can see anything a miss......has the servo acted up at all ? being a JR i would just send it back and see what they say if u have a spare to use in the meantime.