I just finised my first cnc and faced with this annoying noise. I tried to make mdf closure but dont remcommend it. I beleive wooden materials let noise to outside. I tried a big cartoon box and adhesing agg carriages in it. these are low quality cartoon boxes to carry eggs. I saw them once on television, they used it for noise isolation in basement misic works.
these works fine and increadibily reduces noise as I can hear. but very huge noise also comes from bottom. metals and woods conducts noise so every table, table foot lets noise go to room. I tried to put cnc on soft plastic pieces to prevent noise go directly to table. you dont beleive but I could hear the noise reduction. (I dont have dbmeter). I will also put these plastics under the table. but even from a 1cm space between cartoon box and table there comes incrediaby high noise.
so these are for just ideas. if you find any solution please post here.