Humming noise

2002 Jeep Grand Cherokee Limited 4WD 4Dr >100k miles humming noise within hours after 120k mile major tuneup performed. Does anyone know what it might be, and why it would now show up after the major tuneup? Could it only be coincidence or could it be something the mechanic did or overlooked to do? The vehilce hums when I turn the key to accessorry, when I turn the engine on, during idling, and no matter the gear set, and when driving, although because of the road noise (vehicle has air leaks in the door frames), it is there but faint. The fuel sending unit was replaced, but not the fuel pump, at least 6 months ago. The noise is heard louder in the back than under the hood. It is heard more distinctly with the removal of the gas cap. Could some dirt or something get caught up in the fuel filter. During the major tuneup, would the mechanic check the fuel filter to see if it needs replacing? The mechanic's print out sheet is very vague as to what he did on my vehicle for a major tuneup. Full check of oils, belts, hoses, etc. is all he did. When I questioned the front girl, she said it says, "full check". I don't think that's right. There should be a check-off sheet specifying all the items for the oil, grease, belts, gages, cables and tubes, etc., shouldn't there be? I usually go to Chrysler, even though out of warranty. I took a chance on a local mechanic because he was recommended as the best mechanics in the group of mechanics where I live.
Thank you.

Defective fuel pump. I don't want to think that...any way,, that's how total fuel pump failure starts,,with that noise.eventually you'll need to replace the fuel pump. if your jeep dies and you do not hear that noise when opening ignition,, the pump is gone. Hey, It happened to me.