Could be pump...could be a clamp at any water connection on supply side...or could be a leak in-between...BUT find it quick.
Good thing your using your water pump and not city water. City water doesn't make noise and its supply is a lot more than your tank.
I would start with hot/cold water connection at sinks and bath and back of shower and out side faucet if you have one. Then pump diaphragm. Then all other easy connections to see and feel. You might even have to install shut off valves to isolate the line giving you problems.
That's enough to keep busy for awhile. If you still can't find it PM me and we'll go to step 2.