man, i feel for you; i fought this problem So hard for 5 years... on video i could clearly see that i was "clutching" my arm into my body.
i agree with Neil: change your stance. for me, i had to abandon what Mark Wilson calls the conventional stance and go to a semi-snooker stance, feet almost perpendicular to the line of shot. Darren Appleton uses a similar stance, again, it's not quite a modern snooker stance, but much closer to that than the standard pool stance.
for me, it also had to do with trying to do too much with my body and not letting it come Just from my arm. relaxing my grip (no, More than that, like, let the cue go completely at the end of the stroke) helped with that.
the good news is that you Can lick it -- i haven't got a trace left. good luck!