Guys,
Thanks for the help. The glitching is happening before or at the speed control - I know as the lights on the Q2 go a bit crazy when the problem happens.
So I think what I'll try in this order is:
1. not use the "hyper reactive mode" (or whatever Sanwa/Airtronics call it),
2. then try the noise suppressor thing (I'll use Much More rather than Yokomo as they are more readily available where I am)
3. I will try the big worlds kit type capacitor