I work in a government agency building, less than 10 years old, built to some kind of 'green' standards.
When I am in a men's bathroom, either at a urinal or a commode, when someone flushes a toilet, either in the men's, or even in the women's next door, it sounds as if water is being flushed down the floor drain at the same time. (In fact, it sounds like the flushed waste is going down a drain, although that is (obviously) not true.)
Why is this, and what is happening to cause this?
Per a comment: Yes, the sound is coming from a floor drain
(It happens in all bathrooms on all floors of the building. The audible whoosh/splash sounds immediately following hearing a toilet flush. It's easier to hear in 'our' bathroom when a person in the other bathroom flushes, but it also happens when our toilets/urinals are flushed.)