Step 1: Start by placing a button near your door
Step 2: Dig all space by 2 block in front and at the sides of your door
Step 3: Place Redstone near the button
Step 4: Place a Repeater and 2 redstone blocks and another repeater and one redstone block
Here is a fact: Noteblocks don't work if there is a block above
Second fact: Different blocks below the noteblock create different sounds
Step 5: We will use gold
Third fact: Every repeater setting changes the speed of the noteblocks for example the slowest amount will make it so it rings slow
Step 6: The left noteblock must be 4 steps higher and the right one on the lowest setting
Step 7: set repeater to maximum delay
Step 8: Cover your Redstone.
Now click the button and it should work!

Note: if it does not work go to this video: www.youtube.com/watch?v=TFLNUlu_17E