Peafowl, including peacocks and peahens, are known for their spectacular displays of feathers and calls. While they do produce vocalizations, the "sonic boom" noise you mentioned is not directly related to their vocal abilities. The sound you're referring to is a result of a combination of factors, including the structure and movement of their feathers.
When a peafowl, particularly a male peacock, spreads its vibrant tail feathers, it creates a striking visual display. However, the sound associated with this display is not caused by the feathers themselves but rather by the movement of air as the bird flaps its wings vigorously. The large, elongated feathers on a peacock's tail, called "train feathers," are highly specialized and have loose barbules that can vibrate in response to air movement.
As the peacock flaps its wings, the air passing through the gaps between the train feathers creates turbulence. This turbulence interacts with the loose barbules of the feathers, causing them to vibrate rapidly. These vibrations produce a distinctive rustling sound, which some people liken to a "sonic boom" or a rattling noise. The unique structure of the peacock's feathers, combined with the rapid wing movement, contributes to this auditory effect.
It's important to note that the sound produced by peafowl during their displays may vary among individuals and can be influenced by factors such as the size of the bird, the specific arrangement of the feathers, and the vigor of the wing movements. Additionally, peafowl vocalizations can also accompany their displays, including calls and vocal signals that they use to communicate with each other.