A couple of the posters maybe on the right track here. If your not seeing any water dripping or any puddles, you may want check the hot water tank isolating valve(s)... the ones you would close/open to isolate the tank when winterizing the water system. The valve(s) may not be fully closed/opened, or are as posted may be leaking.
If the safety valve is indeed leaking, you will see water dripping/spraying from it or even see steam vapours and/or hear air escaping from the safety.
As asked, do you leave the pump on all the time, if so does it run fairly constant? That'll tell you if you have a leak.