Okay, i'm at my brother atm and it turns out you're right, the problem is still there.
I checked the credit switch and that seems to be hooked up the right way, also when i disconnect the wires the sound is still there!
I made a little sound clip with my telephone:
mario_bros.mp3 - 0.24MB We also switched the faulty orange button with one my spare blue one, looks a bit better.