You are all right, this knocking is "air hammer".
I installed a bleeder valve on Southbound. This was just a “tee” fitting with a valve on the open end, inserted in line just after the pressure water pump. To bleed the water lines, you open the bleeder valve, and let the pump run until you get “airless” water.
Without a bleed valve, open up your plumbing
pipe/hose at the lowest
practicable point, or the nearest
open faucets one at a time, starting at next nearest,
and run till airless.