Some time ago I was driving with my rear seats down and I heard a steady
tone that appears to be coming from the rear of the car.  Now I hear
that tone in the background with the seats up.   It's a constant pitch
regardless of engine/vehicle speed, and only fluctuates slightly if
there is a power surge, such as the power locks locking, so I feel it is
electrical in nature.  The only thing that is back there that I can
think of is the fuel pump.

The pumps sounds normal when I turn the key to ON and it pressurizes the
fuel system for a brief moment.  Also I can sometimes hear it going
through the leak detection sequence when starting it with the engine
cold, a normal sound since the car was new.  My car has the California
emissions package since it was originally delivered in a state that
requires CA certification.  For the '99 (and a few others) model year, a
leak detection pump was used; I think later years used another
technique.

Has anyone else heard the fuel pump make a steady noise?  Is it a
problem?

Thanks!