Thanks for the input. (Scary stuff for us 2.7 owners, ronkent!)
The record played that caused the crackling was probably the most dynamic recording I've ever played on the Thiels. I didn't really know how loud it would get and usually I have a volume control right near me ifI think things are getting too loud. But I didn't want to ruin this gentleman's listening experience by suddenly dropping the volume.
Anyway, the speaker seems fine. I generally don't listen really loud - about 70 db seems to be my comfort zone, unless I crank it more when I"m listening down the hall. The 2.7s seem to be able to take quite a bit of volume, but I believe I normally play well within their limits.