This happens to me all the time. I think it's just part of the game, to make it a little more realistic. I recently installed BL onto my computer and it's been like this from the beggining. I personally don't mind it, and it doesn't seem to get too loud for me (my BL volume is usually around half). I bet it's just a 3D sound effect, and I actually like it a bit. After all, when your closer to something that's emitting sound in real life, it sounds louder, right?