Hey thanks. There was no ice forming on any part of the exterior pipe, which would have indicated a crack. The weather warmed up today and the ice blockage melted. We believe the initial overflow of water into the wall was caused by a water backup from the blockage and a poor seal on the toilet. We'll be replacing the toilet (long time coming) and obviously adding a new seal/gasket/ring. We know what to watch for next time a cold snap hits. Thanks for the reply.