Charlie, I don't think that the storm windows will give you much in the way of sound proofing. However, if you really want to get rid of the noise, you might try styrofoam sheet insulation, You can get it in one inch or two inch thick sheets and cover the windows. That will stop the noise since two inches will approximate the 3 1/2 that you probably have in the walls. I'm cheap and often block off my north windows in the winter with styrofoam. Hate those noisey neighbors. If ya'll are close friends and it's the compressor that's making the noise, you might see if he will install a compressor blanket. That should cut down on most of the noise. Good luck.