I'm no pro or servo guru but I see this A lot with my own stuff, the digitals are the worse for the HUMMMMMMM. All it takes is that little bit of load on them, just the weight of the control rod. I just call it the nature of the beast and fly with them.
The person I trust to answer your question is Tony Stillman. Tony writes the Radio Ramblings for RC Report Magazine.[Only one worth getting] He also owns and operates Radio South. [email protected] or phone800-962-7802 With A question like this it is always better to get an answer from A pro and not off A net site. Just too many conflicting answers and too hard to read between the lines.