noises in the radiator

Kurt_5

I have a two pipe gravity return steam heating system. A new boiler was installed 15 years ago. At that point I new nothing about steam heat. After reading some of Mr. Holohans books I have learned alot.
I now know the installers incorrectly piped the hartford loop, undersized my header and equalizer and didn't insulate my pipes. Now I'm trying to find someone qualifyed to change the near boiler piping and not in copper. I have insulated the pipes myself but find that my downstairs radiators now have water hammer. I have changed the thermostatic traps on all of the radiators. Things got better for awhile then the hammer returned. I then checked to make sure the radiators were pitched correctly and standing straight up, this also helped but once again the hammer has returned. This is were it gets aggravating. In ten to fifteen minutes after the boiler stops a serious snap echoes through the downstairs radiators. Can anyone tell me why this is happening and what I can do to stop it.
Thank you
Kurt