I have finally found the duct work that makes noise when the fan on the furnace shuts off. It is found just above the actual furnace and would be a pain to take out. The sheet metal buckles when fan is on and then retracts when fan shuts off and makes a bang noise. My question is, can i crease the metal somehow with out taking it out ??? or is there another way of keeping the metal from buckling without creasing the metal? any tricks of the trade

Thanks