My house water pressure regulator has started to make a high pitched 'whine'
whenever the water is on somewhere in the house.

I put a pressure gauge on the outside hose bib, without any water running in
the house, and the pressure gauge showed 118 psi.

I opened a bath tub's hot and cold faucets, and the pressure dropped on the
gauge to 48 psi;

I then also opened the second tub's hot and cold faucets, and the pressure
gauge dropped to 28 psi.

I'm confused as how the pressure regulator is suppose to work; and isn't an
initial 118 psi a tad bit high?

Anybody out there know anything about these things and give me a bit of
direction?

Thanks in Advance,
Charlie