Damn! Doh! and everything else.
I discovered today that the Right flipper switch has a 0.1uF greencap (supression) across it, and the Left flipper doesn't.
I added a 0.1uF onto the left flipper switch and
Tah-bloody-Daaah 
! it's now silent!
No more false triggered sounds anymore.
It's reduced from 9/10 false triggers to 0/10 when hitting the flipper switch constanly for 10-20secs or upto 1 minute.
Yay Yippeee
The caps aren't shown in the manual, i can only guess this was a mod from previous owner(s) ???
I won't forget this in a hurry ;-)
Thanx for everyone's input anyway.....
Marty
