To be honest, without a picture to show how you have it mounted, its going to be really hard to help you. Based on what you have described, it sounds as if you have your snare trigger mounted in such a way that it is cantilevered way out off the "L" rod mount. Plastic clamps can only hold so much. If it's cantilevered out, and you are a heavy hitter that uses heavy sticks (i.e. 5B), yes that snare is going to move. I would try using a lighter stick (5A) and readjusting the trigger so it sits more over the center of gravity of the clamp. If that doesn't work, get a snare stand. I don't like having my hi-hat or my snare attached to the rack. Too much crosstalk adjustments to deal with anyway. I hope that helps.