I had a mini bike in the seventies that had a piece of chrome 2 inch pipe behind the muffler. There was a piece of expanded metal rolled into about a 1 inch tube, wrapped with fiberglass that I could install or remove. There was a sheet metal screw on the bottom to hold it in place. It sounded like a hot rod with the baffle removed. It was really quiet with new fiberglass installed. Hardware cloth would be easier to bend. The chrome tailpipe was under the seat, about 18 inches long. you can buy a chrome extension like that from most part stores.