On Sun, 6 Jun 2021 04:48:24 -0200, dan wrote:

I think I found the source of the hissing which seems to be an air flow on
the pipe that connects to the bottom of the pressure switch. That pipe I
thought might contain water since it comes off the top of the pump but it
likely contains air. It seems to be the pressure that the switch senses.

It's way down at the floor level only an inch off the concrete so it's hard
to tell but I can put my hand there and feel a slight flow of air even as I
can't pinpoint the hissing due to the pump noise (it doesn't hiss with the
pump off).

Put a balloon or a condom on it and see how quickly it inflates.