Have you tried a different motor? Sometimes the capacitors go bad and can cause interference. You might also try a different servo if you have one available.
The Spektrum system may help, but it's not guaranteed.
M03R, M04L, TT-01R Type E, Midnight Pumpkin,
Lunch Box, CC-01 Wrangler, SC10.2FT,
SC10B, Traxxas Slash