Update on my buzzing situation - I took the speaker out of the cab and had my wife play the bass while I held the speaker in my hands. There was an odd sound that appeared to come from the cone surround. When I set the speaker in the cab, this sound became the buzzing that I've been hearing. With the speaker out in the air, it took a bit more volume to produce the noise but it was definitely there. I'm guessing the increased air pressure with the speaker in the cab amplified the problem. I called Mesa and they've been great. They're going to warranty the speaker and are sending me the new one (4ohm) with the understanding that I will ship back the old one within 30 days of the new one arriving. They asked me to pay for shipping which I thought was more than fair. Thanks for the advice and the info on the 4 vs 8 ohm comparisons.