If you hear a buzz from a dome tweeter, it is most likely produced by a voice-coil misalignment which causes it to scrape against the motor assembly (instead of remaining evenly within the magnetic gap) when driven, although it's not impossible that something like a bad solder joint at the driver or in the crossover could also produce similar symptoms. The first thing to do is make sure that the sound actually does emminate from the speaker and not from the signal being fed to it, so if you haven't already, swap your speaker cables at the amp end so that the other channel signal is now being fed to the affected side - if the problem resides in the speaker, the symptom shouldn't switch sides along with the channels. Conventional dome tweeter asssemblies (either the whole driver, or sometimes just the voice-coil/dome part, although in your case you can't really be sure the problem might not reside in the motor alignment itself, which could be negatively affected during shipping, although that's less likely than a problem with the former) are often not that hard to replace yourself, and usually not terribly expensive. But the B&W's tweeter is not all that conventional, so I'll defer to anyone with direct personal experience. And you can always contact the manufacturer or distributor. In any case though, you should enlist the aid of the member you bought it from, and see whether shipping insurance reimbursement can be claimed (but that's tough if the outer carton was undamaged).
