There is also an easy way to open the Note Doors (without collecting the necessary notes). Again, enter these cheats in the sandcastle in Treasure Trove Cove (after spelling CHEAT):

Open note door 2
THESE GO RIGHT ON THROUGH NOTE DOOR TWO

Open note door 3
NOTE DOOR THREE GET IN FOR FREE

Open note door 4
TAKE A TOUR THROUGH NOTE DOOR FOUR

Open note door 5
USE THIS CHEAT NOTE DOOR FIVE IS BEAT

Open note door 6
THIS TRICKS USED TO OPEN NOTE DOOR SIX

Open note door 7
THE SEVENTH NOTE DOOR IS NOW NO MORE