Bigalt -The solution is one of the wireless ( rf not infrared ) remote switched outlets that you can buy online. Press a button on the remote and on goes your compressor. Another press and it's off.....
Bigalt- thanks for the recommendation on the remote. A friend also pm'ed me about this remote upon reading my encounter with the troll. :^)
he sent me this link
I am very sensitive about what I plug into the wall. It all goes back to the main panel. My gut feel is I may be substituting a Troll** for a Gremlin, if I added that device between the pump and the outlet.
True Story
When finishing the 2nd adjacent music room there was this hum (aka Gremlin). I thought it was an amp issue. But when the amp was off it was still there. Go figure... I traced it to the door bell transformer mounted and plugged in along side the ceiling joists. I pulled the wires. Noise went away. Silence between songs.
** I later discovered the identity of the Troll. Our 20 year old son raiding our basement freezer early in the morning on his weekly food rampage. Freezer is plugged into a different outlet separate outlet :^)