Are you suggesting that he move his cabinet out of the house?
LOL well that's one possible solution but it may be louder outside than inside.
Buy a supply of the heavier furniture blankets ( available from several on line sources in various thickness) and drape the room with them. Double drape the windows and fill the window frames with sheetrock.
I solved a similar sound issue with that solution and filled the window frames with double layers of 5/8" sheetrock, then blanketed over them and it made a huge difference. If it's a garage, also insulate the garage doors. You can by garage door insulation kits at Home Depot or Lowes...they'll ship it to you. Easy install...cut to fit the panels with a box cutter. I did a 3 car garage in about an hour.
That will not only help with the sound but lower the summer heat in the garage and help keep the winter cold out.

