The best way, for me, is that with the power on...you move the collective up...and push the cyclic stick around..hold it in any position and then gently pinch each control rod and see if it wiggles easily...place the collective down and do this again...if the control rods are all nice and free then the links are ok.
The Balllink sizer is a good idea...I was stuck for one so used a spare ball screwed into a broken rod assy...I scored across the ball with a stanley knife. Be VERY careful when you do this. The resulting scores will easily scrape the inside of a link....just rotate back and forth...not too much...place the link together and see if it moves easily.
The chattering noise is OK...as long as it dies out when you release the sticks...Digital servos do digital things
Hows things with the 90 by the way?
Rob