We had the same problem (drops) on a T1 at another station in town. In that case, the line would lose sync and drop a couple of frames, resulting in a dead spot in the audio till it reframed. We had to run a test set on the line for about a week, and show the telco gerbils that there was a repetitive problem. They still dragged their feet over it, because in that case the trouble was a DS3 line between two central offices, and theyhad to replace a LOT of expensive stuff to make it work properly. The telco wants to say well you have 99.9999% relaibility, and such a drop only moves the last digit to like a 5. Unfortunately, with audio, you can't tolerate >any< frame drops.
Even if that is their problem, it may well be in this economy, they haven't sufficient people to let one sit and watch the thing over itime; or the budget to rent or putrchase a test set they're far from cheap).