i am using a 15" mesa boogie cabinet, and have been playing for quite a while, but i just noticed how much the speaker moves i.e. pushes forward while playing at mid and high volumes. i tried a friends eden 4X10 cab to compare and the 10's seemed to bounce around quite a bit as well. i am using an ampeg preamp (SVP) and a qsc poweramp (rmx 2450) and am pushing it pretty hard, but no clipping occurs. is this normal? something i should be concerned about? thank you for any input.