We had a Princess and the Pea situation in our house in which a moderately quiet A/C condenser next to a bedroom was deemed too loud, especially when clicking on. This is a high-end Carrier-built unit, so it is somewhat louder than a Japanese split-system, but quieter than almost anything else U.S.-built.
We were able to eliminate the annoyance with a blanket from Acoustical Solutions that we hung on the wall adjacent to the condensers (quilted part facing the A/C unit; smooth part against the wall). We also wrapped one that was roughly the same height as the condenser around the side so as to block transmission to a window. It would be a lot more attractive it we built a wooden hutch around it, but it is highly functional just hung on a metal fence U-post (less than $10 from any hardware store).
We bought the ABBC-13 two-inch thick “AudioSeal” blankets, one 96″x54″ (custom made to have the grommets on the long side) and one 54″x54″. Total cost, including shipping and Maskachusetts sales tax, was $890. We’ve had them outdoors through one New England winter and they still look good.
Leaving this here in case anyone is searching for a similar solution.