I own an upstairs condo. Our master bathroom is directly upstairs from our neighbors' master bathroom, so our toilet is directly above theirs.

There has been a noise coming from the area of the toilet that sounds like rushing water downstairs -- as though they were constantly flushing it again and again, 24/7. You can feel the vibrations in the little pipe that goes into the toilet to fill it, even when the valve at the wall is turned off. The toilet is not making any other noises, and there are no tank sounds at all or even any moving water in the tank when the toilet is not in use. The toilet in my condo flushes normally and behaves entirely normally.

Only once have I heard the noise stop, and it seemed to be when the people downstairs did something with their own toilet.

So what I'm trying to figure out is: Is this noise coming from downstairs? If so, why would I be able to feel the vibrations at the base of the toilet here upstairs? Do I need to be concerned about the pipes or a possible leak in the wall?

This has been going on for a few days. Today it seems louder. Any help would be appreciated!

Possibly a common water supply pipe. They probably have a bad flapper causing the toilet to run constantly. If you just pay a common water bill they wouldn't see any change. If your toilet flapper is good no worry.