Noise in 1998 Lumina

Hi all, I'm new on here and doing some troubleshooting on my 1998 Lumina. Recently I've been hearing kind of a "humming to faint whining" noise (It has never gotten shrill) when my car is idling and driving slow. Not all the time but getting more frequent. My first intuition was heater fan/motor, but the noise isn't as whiney as when a heater fan would usually make, so I've eliminated that idea. It's coming more from underneath the hood. Once in a while when the car is idling you can actually hear the noise kind of "kick-in."
When I had the car serviced just a week ago it of course wouldn't act up then, but one of the mechanics suspected it could be a faulty fuel pump. Any information would be appreciated.

That would make sense it being the fuel pump. One thing you can do, when you hear it acting up, pull into a gas station or whereever you are and climb under the car between the rear wheel axles. You'll be able to hear the fuel pump up in the gas tank.

If it is the fuel pump, you might want to get it replaced asap. It really sucks when your at walmart or somewhere and your car won't crank due to the fuel pump not delviering fuel.

When the fuel pump goes out, your car will crank and begin to spit/sputter rapidly, then die.

Thanks for the info, and I will try your suggestion. As I am far from a mechanic, when you say I will "hear the fuel pump up in the gas tank," do you mean I should hear the same type of hum? A friend suggested I take off the gas cap and listen, but I can't do that as I have the safety cap and supposedly the car won't start, or won't run if the gas cap isn't on properly.

I don't know about being able to do it with the gas cap off, but I know you can go it by going under the gas tank to hear it. Another way would be to climb in the trunk and put your ear on the floor. You might be able to hear a hum that way.

The fuel pump should have a steady hum to it.

As for the car not starting without a gas cap, I've heard that the check engine light will come on in this situation, but I've never heard about the car not starting