Actually, ball hiting rubber/metal/plastic/glass have a default sound, so has the drop target RESET Solenoid (drop target down sound is missing => TODO).
Here are all the defauklt sounds that yoiu can modify using some imported from fp:
SetDefaultSound("BallVsRubber", "rubber");
SetDefaultSound("BallVsMetal", "metalhit");
SetDefaultSound("BallVsPlastic", "collide9");
SetDefaultSound("BallVsPlayfield", "glass_hit");
SetDefaultSound("BallRolling", "ballrolling");
// On/Off solenoid sounds
// ----------------------
SetDefaultSound("SolenoidOn", "solenoid");
//SetDefaultSound("SolenoidOff", "");
SetDefaultSound("BumperOn", "bumper2");
//SetDefaultSound("BumperOff", "");
SetDefaultSound("DiverterOn", "diverter");
//SetDefaultSound("DiverterOff", "");
SetDefaultSound("SlingshotOn", "slingshot2");
//SetDefaultSound("SlingshotOff", "");
SetDefaultSound("SpindiskOn", "solenoid");
//SetDefaultSound("SpindiskOff", "");
SetDefaultSound("AutoPlungerOn", "solenoid");
//SetDefaultSound("AutoPlungerOff", "");
SetDefaultSound("FlipperOn", "flipperup");
SetDefaultSound("FlipperOff", "flipperdown");
//SetDefaultSound("CoilMagnetOn", "");
//SetDefaultSound("CoilMagnetOff", "");
SetDefaultSound("DropTargetResetOn", "solenoid");
//SetDefaultSound("DropTargetResetOff", "");
SetDefaultSound("KickerOn", "solenoid");
//SetDefaultSound("KickerOff", "");
SetDefaultSound("KickerIn", "scoopenter");
SetDefaultSound("KickerOut", "scoopexit");
SetDefaultSound("KnockerOn", "knocker");
//SetDefaultSound("KnockerOff", "");
SetDefaultSound("PopUpOn", "popup");
//SetDefaultSound("PopUpOff", "");
SetDefaultSound("PoweredGateOn", "solenoid");
SetDefaultSound("PoweredGateOff", "solenoid2");
SetDefaultSound("EMReelSpin", "reelclick");
SetDefaultSound("SubwaySolenoidRelease", "solenoid");