Thanks, Neil! I'm almost certain the click originates from the bottom bracket, after it was reproduced easily by a mech at another shop (he stood on the bike, stationary, and pedaled backwards in short increments - at certain sections of the revolution the click was loud and obvious).
I use toeclips; the pedals and chainring bolts are lubed and tightened twice over.
I'm going to leave the bottom bracket cleaning and treatment to the lbs. The bike is new, and if they can't solve the issue I'm not sure what I'll do next. So far the level of service has been such that I'm having misgivings about returning there.