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Over the years, tenants of a red brick residence in the Kips Bay neighborhood of Manhattan had begun noticing a growing number of people with suitcases cycling in and out of their 18-story building every weekend.

Many residents said they often heard the sound of luggage being rolled down the hallways of the 126-unit building.

The most observant tenants speculated as to whether some of the people they had seen in the building were tourists who had booked apartments through Airbnb.

“I kind of figured there were Airbnb’s here,” said Kristi Muniz, 26, a consultant who lives in the building on 230 East 30th Street. “I always see families with suitcases, but most residents in this building are post-college or in nursing programs. I even recently told my neighbor ‘I think our neighbors are an Airbnb.’”