300ex rear axle moving

hi everyone having an issue cant quite figure it out , when i put the 300 ex in gear and let the clutch out i can see the rear end shifting a little, not sure if its swing arm bushing or an adjuster bolt i cant seee, i jacked it up i can move anything by hand or see anything loose but something is weird. it does the same in reverse. any help appreciated, this is a low hour machine that sat for a long time outside.