I just ran a new water line to my home. Replaced 3/4 poly butle with 3/4 pvc. Almost immediately started getting water hammer. It only happens when you run the water not when shutting it off. I can turn down the flow at the gate valve and it will stop but as you turn it up I can set it where the water keeps running in the kitchen but I can here the regulator cuttung the water on and off. I mean I'm standing right at it the gate valve its just a foot from the regulator and you can hear the water flow going on and off at the regulator. Is my regulator bad or is there air in my pipes?

You don't have water hammer. Water hammer is that big bang you get when a fast acting valve such as a toilet, shuts the water off. Most likely you have dirt or trash in your pressure regulating valve. Disassemble and clean the PRV.

Turn the adjustment nut on your PRV 1/2 turn... any direction. Close and open your main water valve...

Loud sounds are generally caused by faulty Pressure Reducing Valves (PRV). Chances are may be crap inside the valve, disassemble the prv as Harold suggeted or replace it, also make sure to check the water pressure, good luck.

John