HI to you all.
Here is what I did many years ago to make my mower run as quiet as a sewing machine.The machine was a very old Hayterett with a 3 HP briggs and stratton engine.First I had to identify where the noise was coming from.Most of the noise was from the exhaust and the rest was general mechanical noise.Here is what I did.First I dismantled the engine and reprofiled the exhaust cam to give a much slower lift allowing the products of combustion to escape slower.I then connected the muffler outlet to discharge under the mower deck.Next was the problem of mechinical noise.There is a product on the market called Barofoam,this is a product to attenuate noise and is used in the Air conditioning industry to line the inside of ducting.With this product I lined the outside of the blower housing and the complete top of the mower deck and like I said it runs just like a sewing machine.No more ear plugs for me now.