Yep both have the same sensitivity setting. There are also settings for free standing, wall or corner and they are both set to wall.

Update: I had emailed EA back to remind them that only one speaker buzzed, and they just emailed me back to say they should take it back to have a look. So they're sending me a shipping label. Hurrah!

This is almost certainly a flubbed repair job. Hopefully the technician will be able to reproduce the problem and figure out his mistake. Chances are they did not replace the amplifiers with original equipment, but instead used generic replacements. There could be issues with product quality in the cheap amplifiers they stuck in there, which they probably chose at random from Parts Express.

I'm hoping that's not the case Bit! I think of EA as a reputable manufacturer....if however they did use generic amps, is that going to have much of an impact on the sound? 

It could definitely have an impact on sound, as well as that problem with volume imbalance that you were talking about before.

The difficulty is I have no idea if they really have put inferior amps in there. My initial impression of how they sounded was that I was going to have to redo my ARC2 measurements because something sounded a little "off."

Is it feasible to open 'em up to see if the circuitry inside looks identical in both?

Difficult to get 'em open...and if they did use inferior generic amps then I'm pretty confident they would have put them in both monitors. 

Don't open the monitors or mess with them at all. Send them back and tell them they were not correctly fixed. If you monkey around with them they can say that you messed them up.

If your sending BOTH back remember to clearly mark the one that buzzes. Something like an index card saying "This is the one that buzzes."  You can't be too careful, make it idiot proof.