Playing in my Zen garden I sometimes collect 20-30 coins, and they tend to make very melodic tunes. Do the coins play the notes of a particular song or is a random note played each time? I've tried collecting them with different beats to reveal a song with no luck, maybe someone with a larger zen garden can figure it out?
I emailed Popcap to ask, and they said the following:
There is no music to the coins, they are just all random notes. So if you are hearing music, that's pretty cool and means you have a good imagination or ear for melody.
I played the game to death, unlocking every single thing in it and I also tried to find a pattern to picking the coins up. From what I could tell, they're just different notes that link well together.