We recently moved into a new house with a 3 prong dryer outlet.

The smart thing to do here is replace the 3-prong outlet with a 4-prong, adding
the necessary ground wire from the service panel if needed. With all the
electronic controls and doodads on new appliances these days it makes sense to
get stray currents from static electricity or whatever diverted to a positive
ground muy pronto.
Of course, you could add a grounding wire to any handy metal plumbing if you
are sure there are no plastic piping interruptions in those lines. Your choice,
and good luck.

Joe