My sump pump runs once a minute and need to make something to cover it to insulate and quiet it down. the constant running of the pump is annoying and can be heard two stories up any help would be appreciated.
What Dave said and once more. The key to quieting sound travel is airspace. So if [for example] you build your first box 20" square (outside dimensions) as Dave described and you feel you still have an unexceptable amount of noise, then build another just like it but make it 26" square. This should give you about 3-1/2" of air space all around between boxes and the sound will certainly be trapped in that area. The hole project should take only 1-sheet of 1/2" CDX plywood and 2-sheets of 2'x8' blueboard insulation.
I'll leave the size up to you, but you get the idea.
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