I use JR821 servos. I do not notice them chattering. I have forgotten which airplane I have them in. You have got me searching.
I have been building and flying R/C planes since 1978 and control line planes since 1956. My first radio was a 1978 Futaba 6ch. Over the years, we have had to deal with chattering due to dirty pots, overloaded servos, poor range, RF interference.

I currently have a JR XP9303 with a Spektrum module and one with a 72Mhx Synthesizer module. I also have a Futaba 9CAP with a Synthesizer module. The non 2.4 receivers are all PCM.

Except for Digital servos that Whine, I do not remember having servos Chatter any more. The PCM receivers go into FailSafe, if the signal is lost, so the servos go to Preset positions or just Hold. With non PCM receivers, the servos would chatter if there was Interference or if I was past the limit of a Range Check.

I use mostly Hitec analog and digital servos. I have Futaba 3114 serovs in my Electrifly Seawind. I have Eflight servos in my Eflight Extra 260 flat foamie. The Hitec digitals are in the 87" Extreme Flight Yak54, the QQ 72" Yak54 and my Kangaroo jet. I have JR servos in my H9 P47-150 as I bought it with servos installed.

I do not have anything against Futaba or JR servos, I just have had good luck with the Hitecs and saved some money.