I have sorta the same issue, my lights will flicker sometimes, just on and off for no reason, i suspect that i have a minor short somewhere that trips the little ciruct breaker in the switch or something, my grounds are good and it doesn't happen because of bumps or anything, it seems to auctually happen when i'm going slow, as if they can't cool down?? I've just decided to ignore it for now (it doesn't happen half as much) so if you figure out what's happening i'd love to know. one thing i did do was drill little holes in the bottom corners of my lights because i noticed i had some condensation in there (auctually a puddle...) and that seemed to help a little... but i'm not sure.
Good luck!
-Bart