This has occured in the past for some other posters here. Two things could be causing it: either the driver is not screwed in tightly enough, or the shielding magnet inside is loose.
In the first case, you can tighten the screws to fix the problem. If you still hear buzzing, you can unscrew the driver all the way, press the shielding magnet tightly onto the back of the driver, and then replace the driver and screw it in.
Before you do any of this, however, you should call Axiom and ask their opinion. Chances are they will instruct you to do what I said above. If you screw up somehow while following their instructions, they'll most likely send you a new driver for free.
