Coming from a financially upper middle class background, having had a Classical education, and holding significant estates in Devon - ergo, being, for all intrinsic purposes, upper class - I have never, until recently, been under the impression that Metal, of any kind, is associated with the lower classes. It had never crossed my mind that metal had been a part of that whole class divide nonsense, indeed. I knew, of course, that early metal bands (Black Sabbath spring to mind instantly) came from lower class backgrounds. However, the bands of the early Norwegian Black Metal scene were, as far as I know, middle to upper middle class. Look at Akercocke - an obvious sign that Metal is not simply music for the "brutes" of society, as friends of mine have so politely put it.
Conversely to my own class background, a cousin of mine has most notably taken the appearence and affectations of a member of the lower/lower middle classes. He, too, listens to Metal predominantly. I find it interesting, however, that he is more inclined to listen to the heavier, more aggressive, and more popular styles of metal. Bands like Hatebreed, early Slipknot, Korn, etc, feature on his list of favourites. He was, at one time, an avid fan of Children of Bodom, but, unfortunately, that foray into European Metal ended rather abruptly after the release of "Are You Dead Yet".
It is my belief that Metal, being so diverse a musical genre, can engender interest in any individual, regardless of class. However, when it comes to subgenres, there can be clear class distinction. I tend to find that the more eloquent and better educated fans that I talk to tend to listen to the more technical/musically interesting bands - Decapitated, Emperor, Dream Theatre, etc. Black, Death, Progressive, Power Metal. Those with lesser intelligence (or, perhaps, those who simply choose to have an inability to type proper English or use correct grammar, syntax, vocabulary, brain power, etc) tend towards what I would dub the reflections of popular music - bands like Slipknot, Atreyu, Avenged Sevenfold, who are most certainly "mainstream", and far closer, musically, to "traditional popular music", if such a thing exists.