I am not a physicist so take the following analysis with some degree of reservation, but I thought I might have a look at one of the most talked about comic book pictures of the last month from a different vantage point, and that being from a physics standpoint. Starfire is over 6 feet tall but in this picture her hair is moving in a relatively circular motion, thus making it relatively easy to approximate its length. Seeing as she is standing partially in front of her hair the portion behind her will appear smaller, thus while it is not an exact measurement we can say that her height is roughly the diameter of the circular hair flip, but not quite, so somewhere in the five and a half feet area. This would give her hair a length of about 17 feet (achieved easily enough by multiplying 5.5 by pi).
When hair is wet the reason for its uniform behavior is because of the molecular bonds between the water molecules and the hair follicles. Also as hair tends to be of different lengths the number of hairs reaching to the same overall length as 17 feet would be less than the number of hairs reaching fewer feet. This is all to say that Starfire’s hair would in essence act like a bullwhip. Bullwhips generally don’t work in long circles though, and that is because of rotational momentum. This can be observed any time that a significantly long piece of string or chain is spun around. If spinning at the center is slow then the portion on the outside will not necessarily have the speed to maintain a tight string. However, the speed on the inside in the case of Starfire is sufficiently fast to allow at least the full length of her hair to spin (and in a near perfect circle.) For those who think that this is an easy task, try spinning a 17 foot long piece of rope (and spin it from rest all at once, don’t let a little out a time) and see how hard it is to get the whole thing moving, let alone in a circle (though someone really fast would theoretically get it to be almost straight.) Suffice to say that Starfire has some really strong neck muscles to pull off this feat.
What happens to the hair though? A bullwhip works is constructed of a tapered piece of material (usually actually two piece, the top is leather the bottom is braided string) which when used properly creates a miniature sonic boom (which is the sound you hear). The method of how it works is that the momentum carried forth by the speed of the flicking of the handle carries forward into the smaller portion of the whip and with an smaller mass but with the same momentum (this operates primarily under the conservation of momentum) the speed increases dramatically. It should be noted though that tips of the whips rarely move in circle motion, rather they move more or less directly between points. Computer models were shown in 2008 to indicate that the dinosaur species, the Apotosaurus could potentially have whipped its own tail thus create the sound more akin to a cannon than a bullwhip. Bullwhips will be relatively short usually at around 4 feet in length but can top out in length at about 14 feet, thus 17 feet is in the middle somewhere both in strict terms and also because the length will be inversely proportional because there are more than one variable in play here. This is all to say that after Starfire used her massive neck muscles to create her perfect circle of hair, the sound made by doing so would probably been loud enough to be heard from some distance away (that would even be true if my estimate is off by a couple of feet because the hair is moving fast enough to be in a circle).
Again I am not a physicist, and these were just some random observations. In closing though I can say that the caption in the panel "There is a God" is applicable here. As Mies van der Rohe said "God is in the details" and so whoever was witnessing this must have been a physicists interpreting the laws of nature in motion