Rick,
I don't have a Seeburg manual in front of me right now, but check yours
for the stacks of contacts in the mechanism section. There is a contact
specifically for the popularity meter (buzzing twice), and another one
or two that must make just before another set makes....otherwise it
will reject immediately.
It's good you checked the safety plunger....that indeed can cause an
instantaneous reject problem. Certainly it is not the only cause.
Also, determine if the reject occurs because of electrical (contacts in
the mech stack), or mechanical, which could indicate a bind somewhere
or even the clutch not dropping into play, and revolving around
completely to go back into scan. This can happen due to a dry clutch
which is in bad need of lubrication/oil. Hope this is of some help to
you. Rob