I've had the same problem with lab quality regulators for
nitrogen, argon, CO2, etc. I'm surprised how much gas is
lost through them.

Speechless wrote:

There is always some air loss through the pressure regulator. You
will notice that when you adjust the pressure from higher to lower,
the regulator vents the excess pressure from the hose into the
atmosphere. The venting is why you hear the hiss. That is where the
leak occurs -- the air seals in the regulator are metal to metal and
are not intended to be perfectly air tight; they are intended to be
functional, safe, and robust during normal usage of the machine. I've
had name brand, top of the line, replacement regulators, straight out
of the box, leak more than that.