Go over those optos again and make sure they are adjusted properly.Unadjusted optos cause random activation from vibration while playing a game.
Now for the humming sound try and tighten those screws hold the sound board in place in the backbox.Let”s see if that corrects the issue..post back your results

Ok let’s try this..on that flipper that drops the ball lift up the playfield and do some cleaning on the EOS switch or opto on small flipper board that activities that flipper with a dry rag.Do Not spray or use chemicals just dry.Also,power off the game and reseat the connector on the opto board.it should be located under the playfield.

For the sound...power off try reseating the connectors on the sound board,Then VERY GENTLY push in those sound roms..remember very gently.

Note.Im not sure if this game has a small flipper board with an opto in the right flipper area in the cabinet.let me know if it does or doesn’t have one

This just came to mind are those balls very old or new?Sometimes old balls will become demagnetized over time.Also,clean the magnet that picks up the ball..just use a dry rag and clean the magnet on the helicopter