If you hear clipping (short drop of sound) during a game, flip, multi-ball, it probably means that the voltage drops below 11V.
Please check with a DMM (Digital Multi Meter) the 12V voltage, especially while flipping.
This issue mostly arise on Data East machine: the capacitors on the power board are often dried.
To solve this, change your large capacitor(s) on the power board.
Then, take a look at the bridge rectifier and connectors on the power board.
