Modern solid state games have always had loud knockers, since the coils are rectified, and the plunger thwacks against the actual cabinet--making for a huge resonating chamber effect. The OP is referring to knockers that are used in EMs. They're always really lackluster since the coil isn't DC powered, and they only strike a metal plate that the coil is attached to. Williams was always the worst offender though, since the coils were weak, and mounted towards the rear of the cabinet.

The more I look at it, how necessary would it truly be to even slap that extra diode across the lugs? Considering a bridge rectifier is just 4 diodes, assuming the bridge you have on there is beefy enough, I can't imagine you'd need the snuffer diode.