Folks, been hearing this whining noise for a while now and sounds like it is coming from underneath the truck somewhere. Sounds more like a power steering pump whining when turning too far on my old chevy!

It is loudest when first starting and is quite loud at times. Sound varies in pitch. I have crawled around under the truck a couple of times and could not tell where it was coming from. The resonance seems to throw the sound around.

Once I start to drive, it tones down where it is not noticable.

This past weekend, I decided to top off fuel before I changed state lines and had to pay more. was about 1/2 tank. Topped off and surprised it only took about 7 gallons. Usually it is about 10 gallons per 1/4 on the fuel guage, so I was expecting near 20 gallons.
Got back in truck and fuel gauge was just under 3/4 tank reading! I had the neck full as I didn't think 7 gallons was right, so I was suspecting the gas station pump was not working right but it was full in the neck for sure.

So, now....thinking that this whining noise is the fuel pump........

Anyone had this experience? How difficult will it be if it is the fuel pump?

I have about 144K miles now.

 

I've had a similar thing happen twice:

Both times I only needed "half a tank" and I left the engine running
while I filled up.

Took about 2 days before the fuel gauge read correctly.
Each time I started the truck, the fuel gauge was slightly
more full.

I just wait to fill-up when it's 1/4 tank and shut the engine off.

 

I normally start to hear the fuel pump at 1/4 tank. I cycles on and off. With a full tank I don't hear it. To replace the fuel pump (when it goes bad) you'll need to drop the tank - it's inside. There's at least one post on here with step by step photos.

 

Well, finally got to the bottom of the noise and problem. Not fuel pump afterall. Was able to get pulled in the garage and slide around in good conditions on the floor while truck was running.
The resonance was incredible. First, sounded like coming from the rear, slide back and now it is coming from the front. Slid forward and finally figured it was sounding more like coming from up in the engine bay.
Went topside and pulled hood latch. Went around to front and soon as I was reaching in to pull hood up, could tell the noise now broadcasting from under the hood.
Opened hood, could not tell where coming from. The elusive and mysterious noise was finally.......the alternator! By this time, it was getting warmed up and the noise was quite subdued compared to when first starting up. Put a large screwdriver to the alternator body and to my ear and wow! This is it!

Returned Fuel Pump and picked up alternator. 3rd one in 3 years! Thank goodness for the lifetime warranty on it. Getting tired of these weak alternators and every one of them has a different story.
Autoparts store put test on and it failed for bad ripple. Said it was all over the place and should be steady.

Filled up tank and now the gauge is reading full like normal. No idea why the one time false reading, but I have seen and heard others comment that their fuel gauge sometimes gets stuck, so will write that one off until it happens again.
Just glad to get rid of that weird noise! Glad I didn't have to drop the tank! Glad it was not something worse!

 

Glad it was an easy fix. Agree, mine goes through alts every couple of years. Does your gas tank whoosh (suck in air) when you open the cap?

 

Cool - I was wrong, I would have thought it was the power steering pump from the description. Mine makes a heck of a whine during the winter when it gets below zero, but the synthetic tranny fluid helped cure it quite a bit.

 

I don't recall a whoosh when removing the fuel cap. Should it have one? I know some cars seem to and others do not.