Hear a dripping toilet

I live in a bilevel where the upstairs toilet is right above the downstairs toilet. I can hear a dripping noise into the pipe right above the downstairs toilet. What would be causing this?

Several things: do you ever flush dental floss down the toilet? If you do, some of it might be caught and acting like a wick. The flapper valve miight be leaking. Turn the water supply off, let it sit overnight, then check the tank to see if the level dropped. If so, get a new flapper valve.

Are you sure it is water dripping? Plastic pipe (ABS and PVC) will make noise much like dripping water. the plastic expands and contracts with temperature and if the pipes make contact with the building, this will cause some noise. That's the bad thing about plastic pipes. That said, do what Jim suggests in the previous post first.