Norwalk police and fire departments responded to two underground explosions this morning that blew out windows and terrified customers at one bakery.Lower Main Street between Cross and Wall streets, including Main and Hoyt, were closed to traffic. It was one Big Bang,” said Dorothy Greene, Norwalk Resident. Muro’s Original New York Bakery on Main Street in Norwalk was packed with regulars around 8:30 Tuesday morning when a manhole explosion shook the walls and took the chairs out from under customers.