IIRC there's a well known clunk when the forks are unloaded, eg over a bump.
Unless the bike's been crashed I wouldn't have thought there'd be much difference in the fork action between yours and the demo bike. Has it had a front tyre change do you know? Also, when I fitted a fork brace on a Glee then part of the checks, again IIRC, was to pump the forks up and down to make sure that the wheel / forks etc were in the correct alignment.