We have an over the range microwave with built in exhaust that vents outside through the attic. It is noisy as heck and I want to quiet it. Seems like most of the noise is coming from the front grill where the fan would exhaust back into the room if I did not have the outside vent. Some noise is also coming from the cabinets directly above the microwave as the rectangular metal duct goes directly up through it and into the ceiling.
I have access to some 1" thick very dense fiberglass insulation used in the marine industry for thermal insulation. I am thinking of gluing this onto the outside edges of the metal duct as well and stuffing it inside the space in the microwave behind the grill. It won't cost anything to try, but was wondering if there is anything better that is readily available at the local home depot.