Hopefully there are more to be found. Some of these are more consistent than others but a few that are known of so far:

Ch 1 - near beginning to skip ch 1

Ch 2 - near pipes on truck part

Ch 2 - near crane on rooftops

Ch 3 - before balloon and truck

Ch 3 - coming out of the party barn

Ch 3 - before dropping underground

Ch 5 - before dropping down into factory

Ch 5 - after box conveyor belt

Ch 6 - on top of the log truck

Ch 6 - after the big rock rolls down the hill