Your mileage may vary - - this pack was on it's last legs about 10 months ago, so I stabbed through the jacket with needle probes and gave each cell a couple of jolts from a 470,000 uF capacitor with around 40 volts on it. Killed a few needle probes, and the pack danced about a couple of times. After that it got a dozen or so charge - discharge cycles at 20% C and seems to have regained it's old performance, but it possibly has a bit more impedance than originally. The FrSky module is taking a bit less current so I am still using it, which is probably stupid I know. I might just put 3 or 4 4uF7 tantalum capacitors around the transmitter on the grounds that if the problem(?) doesn't re-appear, I have fixed it. If the problem is back, it is obviously a bad batch of capacitors
It does not seem to affect models in flight - all I have tried it in is a Skyartec Skyfun, with no difficulties then a Multiplex Easy Glider that has two HS81s (down in the tail rather than long pushrods), and 2 HS 55s in the wing. It buzzed a bit while the tail servos were moving, but not really badly. In flight at a somewhat unwise distance and later at quite high speeds for an Easy Glider, there was no noticeable problems. I have just set it on the bench to try with the suspect transmitter battery, now at 9.8 v, and there is no jitter with any servo. I THINK I have everything set up the same as it was earlier except it is a little cooler now. (20.2 C, was around 22 earlier.) I may have less or more computers running than earlier; they surround the bench a bit. If this is going to be intermittent, I will be convinced that evil forces are at work again.
I was going to try switching to low power while the model was flying at a long range, but realised if it was out of range, I might re-set the failsafe to something novel. I usually consider these things while the glue is setting, but this time I stopped just before being stupid.
Tomorrow I may try to see if I can re-create the jitter, I don't know if I want to succeed in that. I will also try with a different FrSky module (non telemetry) but I have never noticed the problem with that module before/receiver. I'll also try with the telemetry transmitter and the older receiver.
Can you think of any other simple tests an old duffer can try?