Even when the cut off valve is turned off to the toilet I still get the sound of running water, but can not see water running.

You should check the flapper inside the tank. It is likely leaking water into the bowl so you can hear it but is runs down the inside of the bowl so slowly it is hard to detect. Leave the stop cock closed for a day and see if the level in the tank drops.

Another easy check is to put some food dye in the tank, if it is leaking it will show up pretty quick in the bowl.
Sound travels a lot in plumbing so I would shut off all the water in the house to see if there is a leak somewhere else that you can only hear at this spot.