Here we go again on the definition of "folk". I'd certainly agree--and say that hard rock by definition is not folk. Fortunately, Rabbi Sol, you have the only opinion that counts. And if they complain, you can point out to them that there are already far more venues that cater to hard rock--and you'd just like to keep one for something else. And you might even mention that quite a few prominent rockers have gone "unplugged" at least part of the time.