Hey guys quick question. Today I noticed that when my car is idle I am hearing a humming sound coming from the rear of the car. But one thing is that currently I am having some idle issues I guess due to the bad O2 sensor on it. When the car is idling normally around 650 RPMs I do not hear the sound. When I am idling the RPM's dip a bit to the 450-500 range and that is when I hear the hum. Could this be a sign of the fuel pump on its way out? The reason I am thinking that is the car was sitting for awhile with stagnant fuel in it and maybe thats what put it on its last legs. How long do you think I could push it if it is the fuel pump?