awalts

It turned out to be the Water Pressure Reducing Valve. I lowered the household water pressure (loosened the valve) and then slowly brought it back to the original pressure. And the knocking went away. I can't explain why it worked, but it did. We haven't heard the knocking sound in over a year.

Wuzzat?

Something may reinitiate it, but at least you know a fix that works for now.

jj_iitk

hi, we have exactly the same problem as yours. Where did you find your water pressure reducing valve? does every house has it?

Shawner

Not every house has one but every house should (if connected to a municipal source). They're typically located right after the main shutoff valve where the water enters your house.

Wuzzat?

You want more than 20 PSI static pressure into your house for sanitary reasons and less than 80 PSI to make the pipes last long.
Max flow rate may be 16 GPM but there may be a minimum for sanitary reasons.