Is that pop bumper activating as soon as you turn the game on before the MPU completes its booting ?
If so, the associated drive transistor on the Solenoid Driver board is shorted and needs to be replaced.
The affected pop bumper coil (and the diode across the lugs) may need to be replaced as well if it is burned and partially shorted - otherwise the new driver transistor will short-out again.
- Sylvain.