I have long maintained the drivetrain design is subject to both forward and backward backlash , so your thoughts make complete sense to me Phil. Cant explain why it only happens to the select few , but that in itself seems to be a Morgan attribute.
Seems odd. Against the backlash idea: when accelerating the drivetrain is not in any slack state. If the rear tyre slips... well its still under load when slipping. Could be the load reduction causes the Centa to wind back a little, and then quickly is reloaded as the reduced torque allows the tyre to drip again. But **** knows where the banging comes from. Clutch slip maybe?