A few years back I remembered seeing something on an ad on tv describing like a box you put over loud machinery like an air compressor so it will become quiter and even silence it. I don't know the name but from what I remember it was a white looking box very large.
You can build a box using 1x or 2x lumber and plywood, depending on how big you need it. Then line the box with either egg crate foam or styrofoam. Both act as noise supressors. Be sure to allow room for ventilation if needed.
foam insulation board,make your own pretty cheap.
