Having the same problem here on a Logitech G35 headset. The grinding/buzzing sound only plays on the promenade. It doesn't happen in Ops or in the areas off the promenade, like the bank/exchange or the shipyard. Adjusting all of the seperate volume sliders had no effect on the sound, and I have not heard it in any other area of the game.


EDIT: I can also confirm that the sound only seems to happen on my aforementioned USB headphones, and not when I'm playing on speakers run off my onboard sound card.