so is it just the exhaust vibrating badly or the whole engine ?
if it bouncing round in the bay like a small kid with adhd that been fed a large quantity of blue smarties i would say. i would say somethine quite magor and mecanical has departed what it was attached to.
if it's not quite that bad ( and more likely ) it may have dropped a cylinder for some reason. pull the plugs have a look at them, read the fault codes and do a compression test
