I get the over charge chatter from only one of my planes and it happens every time after a full charge. The servos that do this are high end JR digital servos. After one quick flight this condition goes away and doesn't happen again unless I give the battery a fast charge. That's pretty normal to see. Once flown it is gone. What is see with extensions is when they get dirty the servos start to lag. If not cleaned the problem can get very bad. I saw this at a lot of the IMAA giant scale events. A lot of the big planes don't get flown often and the owners forget or in my case are too lazy to be pulling servos just to clean the extensions. After seeing a lot of crashes of giant planes I started soldering wires to extend my servo leads and no longer have any problems, and I don't have to clean the critters.
With Ys that are having a chatter problem it can be other problems, usually something wrong with the Y itself. I have never bothered to take a bad Y apart and test it to find out what the problem is so I can't say what is going on with them?