To cut down on water pump rumble I built an enclosure out of 3/8" ABS plastic. (ABS plastic is easy to cut on a table saw and glue with PVC cement). Closed cell foam occupies the air space inside of the box.
The foam and box help reduce noise but it's not eliminated. Perhaps the only way to significantly reduce noise is to hang the pump in mid-air.
The gate valve over the enclosure is used during the winterization process. It's a bypass valve that allows me to pull potable antifreeze through the system with vacuum cleaner suction. The intent is that if potable antifreeze is run completely through the system and subsequently sucked out as much as possible, then: