Why do I hear water flowing in a floor drain near commercial bathroom fixtures?
The sound you hear is the “primer” releasing a “squirt” of water into the floor drain. The primer is activated when a nearby water valve is activated. In your case it’s the urinal valve.
The floor drain has a trap that blocks the smell from the sewer lines from flowing back up the sewer lines and into the room and building.
Primers are placed on drain lines and traps because they do not get a regular flow of water to keep the trap full.
Because you didn’t complain about a sewer smell, I know your primer is working.