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!