Clean everything before you mount it. The cup, and inside and out of the rubber boot. Isopropyl alcohol, acetone or even brake clean works well. Pivot the actual airbox around on the boot until it touches the seat or something. That will prevent it from vibrating around unsupported.
Make sure you are actually getting the clamp over the filter cup. You can get it too far too the back then it slips off the back side of the cup and loses tension and off comes the box.