Dear Jeff,


        This is normal and inherent due to the way we pulse the coil for
hold
mode.  Some flippers are louder than others. Sometimes loosening or
re-tightening or removing and replacing the coil stop on the particular
offender will decrease or eliminate the buzz, but if left alone will have no
adverse effect on the flipper itself.


Best regards,
Joe  

Stern flippers use AC power to "hold" the flipper in the upright position.
AC power (as used in older EM pinballs) will cause a hum because it's
turning on and off 60 times a second.  Your flipper is technically flipping
60 times a second in this situation.

If your coil stop is not perfectly aligned (parallel) with the end of the
coil plunger, the hum can be more noticeable.


So hitting it with a hammer (or more likely, gently tapping it a bit) may
very well solve the problem, and it's really the quickest way to solve the
problem, if it's not too major (coil stop *really* out of alignment).


Just use common sense- tap it a bit- don't go wailing on it with a sledge or
anything.  Maybe even tap from one side to the other if it's angled
(sometimes you can visually "see" an alignment problem).  Or loosen the
screws and re-align the coil stop manually, re-tighten, and see if that
helps.


If the coils stop is angled forward/back, you'll need to probably remove it
completely, and bend it either in a vice or hit it with a hammer on a solid
surface to bend, or straighten it out.  Or buy a new coil stop if you're
worried about not getting it to straighten out.


Good luck!


--
Ray Johnson