OK, wrt the 3D signal @3.3Vthat explains why the voltage was actually lower on the signal line and also the reduced frame rate I was seeing on the scope (the Airtronics is very fast).
By 'with or without' I was referring to whether the equalizer was in place or not between the extension and the servo.
It does look to me like the noise is coming off the servo. Ah well time to experiment to see if there's something I can do to smooth that out (maybe add a cap). Maybe Hitec will have some suggestions.
Thanks for the incredible level of support!