If you are using analog and digital servos of similiar power I would not think the control surface weight is causing the problem. Some where I read lots of current draw and or voltage across the receiver power bus can cause signal interference. I fly a GP Pitts with eight analog servos using a 5 cell pack. Once in a while I get the jitters on the ailerons after first turning on the receiver battery. No problems after that. I am going to use an isolator on my 1/5 Wildcat because I want to isolate the current draw of the digital servos. 4 cell on the receiver running throttle and retracts then 4 digital servos running rudder elevator and ailerons and 4 smalll analog servos for flaps from the isolator using a 5 cell. Not field tested yet. Isolators are expensive so try to borrow one and test your application.

Carl