I never had this problem before until I started using this specific cab. It's a custom LDS 410 with duratex finish. I have my heavy SVT tube head on top. Tried with my Ashdown ABM head, same thing. When I play most notes, it doesn't move. When I play C#‎, even at low volumes, the head starts floating off the cab. Does anyone think there's maybe an issue with the cab? I tried doing this without the casters on, put the cab on thick carpet, tried a friend's gamma pad. Nothing seems to help. It not a slight movement, that happens over a set. As soon as I hit that one note, it looks like the head turns into a hovercraft and starts to fly right off.