How do I find the bandit under the hat in room 5

In the old milnery, the pinstripe bandit gang splits up and hides in different rooms full of hats. The first few rooms are easy as the bandit's hats are very different from the rest of the hats in each room (like the lone black hat in the sea of white hats). But by the 5th room, I can't figure out which hat belongs to the bandit and resort to guessing blindly.

How can I reliably determine which hat belongs to the bandit in room 5?

To find the bandit in the fifth room, you go into the main area and access the piano there, then pick the song Public Domain Joe (cotton eye joe reference) to which the bandit starts whistling to, which them makes him easy to find. Also for the other rooms, room 1 is easy, it's the only black hat, Room 2 is also easy, just gotta wait a couple seconds to see which hat moves around. Room 4 is also connected to a song on the piano called My old public domain home. Room 3 is the only room I cannot figure out, and it is taking me a while as I am writing this to figure out the solution.

EDIT I have figured out room 3! The guy in room 3 doesn't have a big dent in his hat compared to the others! Hope I helped everyone out.

Turn the piano on to Public Domain Joe and he will whistle when you go in the room. I got them all but the third.