Just for grins remove your control rod from the servo horn, move your stick to full and there should be no humm, now just go ahead and touch the control horn, not A lot but just A little pressure, bet it humms again. Sometimes just the little weight of A control rod will make them do that. Digital servos are even worse. My high dollar JR digitals are worse then my digital HTs or Futabas, just look at them the wrong way and they humm at you. Always best to check but most the time it's just the nature of the beast. Nothing wrong with the standard servos, just A couple of years ago 48 inch pounds was A lot. I still use my old standards for A lot of things.