This is unofficial advice given neighbor to neighbor; accuracy is not guaranteed, and any work on a unit should be done by licensed professionals with proper permissions from the building management.
If it’s not coming from the street, most of the noise coming into your apartment comes from your neighbors. Adjacent apartments on each floor are well insulated from each other with over 16 inches between your wall surface and your neighbor’s wall surface. On the other hand, the noise separation between your apartment and your neighbor above and below you is minimal. The distance between your ceiling and your neighbor’s flooring is about 3 inches. There is a ½ inch layer of insulation on top of your ceiling wallboard and then your neighbor’s floor. Everything hitting the surface of your first floor is telegraphed to your neighbor below. Recommend whenever you do work on your flooring to contact your neighbor below you. Your neighbor below you will hear you doing the simplest things including when your dog or child runs across the floor.
The up-down sound carry is one of the reasons this building has strict rules about adding a layer of sound-deadening material underneath when installing hardwood or similar types of flooring.
It helps to be considerate of neighbors; if you’re prone to pacing late at night, try to keep it upstairs, or on a carpeted surface and towards the inside end of the unit away from the bedrooms. And please don’t vacuum during the building’s quite hours (10:00 PM to 7:00 AM)—that’s a sound that’s particularly noticeable to the people below you. The flip side is that people should try to have reasonable expectations about noise; kids will be kids and this is a large, city building.
Beyond the up-down sound carry, the fire corridors also transmit sound rather effectively— just something to keep in mind when you’re spending time in the vicinity of your second-floor fire exit.