If its an AM set, the rudder twitching is the prime indicator of interference via the radio, and usually the motor is the handiest source. The receiver is listening in the long quiet bit between bursts of information, and the first signal that it thinks it sees is passed to channel 1, usually the rudder, so the rudder twitches. Less of a problem with FM outfits, should not happen at all with 2.4GHz.
As Dave says, increase to the full set of three capacitors, take the opportunity to replace the existing one since they are pennies, and there is nothing to say whether the original is actually working, and no easy way to test it without specialist gear. Twisting the motor leads as a pair is good too, as is twisting the power leads going to the ESC, since these get the self same current pulses. Twisting causes the interference coming from each wire to be cancelled by that coming from its mate. More or less.
Checking the motor for sparks will help - if the brushes/commutator are sparking it could be a sign that either the brushes need bedding in or the commutator needs a clean, or both. Light brush tension gives the same problem, as does a commutator running out of true.
The higher frequency might give the motor a series of smaller shoves, resulting in less back EMF at the end of each shove, less energy to dissipate, thus less interference. Thats just a guess, though, as are most things interference related, until you get the actual cure, then it should all be obvious. Hindsight.