GFCI tr[pping with no outside load
Turn off the circuit breaker and pop the covers off and pull it out.  Disconnect anything from the LOAD terminals, tape up the bare wires so they can't touch anything, and put it back in the wall. 

Does it still trip?  It's a bad GFCI.   

Does it stop tripping?  It's because whatever was connected to the LOAD terminals has a ground fault... Or the wiring to those things.  You will know what those things are, because they lost power when the GFCI tripped (and also when you disconnected them).  You will need to troubleshoot further by disconnecting one thing at a time until you have narrowed it down to one thing.