On Wednesday, July 30, 2014 5:37:20 AM UTC-5, wrote:
I live in an apartment .... Hmmm, guess I have some things to consider.

In theaters, large thick curtains are used to dampen and prevent echo. Try installing some thick drapes, on 3 sides and over the compressor, to see how that works. Use some thick bath towels or bed blanket for the testing of the drape option. Use dining chairs for the towel/blanket props, and maybe a broom stick, across the tops of the chairs, for draping overhead. You can test this option at no cost.

If the test draping works reasonably well, purchase some thick (remnant! *cheap) fabric (or thick blankets, from Goodwill, Salvation Army) and make a room divider type drape over and around the compressor, leaving one side open (partially open?) for air circulation/ventilation.

Room dividers and workplace/work station (office setting) dividers work well for reducing sound/noise from adjacent areas or work stations.

Sonny