Digitals are known for chattering, particularly the zero dead band .
If you really are concerned, then disconnect all linkages and see if they stop chattering. They should either stop or decrease markedly.

I do not use either Rx you mention but the DSM2 Tx/Rxs chatter the least.
The others chatter more, and that is normal.
The chattering is the servo searching for neutral____a tight neutral____.