Things Mai knows about the Buzz (she may have told some of these things to others):

• Lots of random folks on the street buzz, perhaps more than half. This causes there to be an annoying empathic interference pretty much anywhere Mai has gone in Chicago. Clearly these folks do not have any real empathy, but are still somehow broadcasting this sound, which feels like something is interfering with their thought processes.
• All empaths encountered so far seem to hear the buzz too. They don't hear it as loudly as Mai, since they aren't as naturally empathic as she is (she has a higher EMP score). Like Mai, they've heard it all over Chicago.
• The single worst source of the buzz was Max's monster, the Tulpa. At one point it buzzed so hard that this was part of it's mental assault on Mai in the alley in back of Marcus' bar. The crazy sorcerer Eli who created the Tulpa buzzed a lot too, second most of anybody she's met.
• None of the members of the underground buzz. Not even Spense… until recently.
• Mural Man (AKA the Prophet) buzzes a lot, and his buzz is strange, not like anyone else's. His buzz matches the mixed up buzz found in the neighborhood around the bar, centering on the cemetery.
• Elspeth works at the bar in that neighborhood. She buzzes, but not like the neighborhood… but like everybody else in Chicago other than the Prophet.
• The Ra-stone at the Citadel of the Order of the White Circle buzzes.