What is that noise coming from my truck???

Request help from any gear heads in identifying a noise. I recently bought a 1998 Chevy Cheyenne 4x4 shortbed. When the vehicle is running, there is a high pitched “whining” noise, apparently coming from the rear, under the bed area. But perhaps it coming from anywhere. It almost sounds like one of those high pitched alarms when you leave your keys in the ingnition, and the vehicle is off. However, this noise happens whenever the vehicle is running. It almost sounds electronic. Any clues? Is it something in the drive shaft? rear axle? Any help is most appreciated.

Does it happen when the truck is moving or just idling? If it’s moving it might have a chipped ring gear in the rear end.

My Dodge Daytona did this. It was electrical interfernce that wires running to the back would make ( a non-issue…came and went…just annoying).

I also know of fuel pumps that make this noise. Could be on it’s way out. Real hi pitch and whiney.
Important question: with the key set to “accessory”, engine is off…does the noise still happen?

If only when running, I lean towards fuel pump.

OK, a few things. It occurs when the truck engine is on, whether moving or not. It does not occur when the key is set to accessory. I just went out and started the truck, and climbed underneath. A few observations: The noise starts a second or two after the engine starts. It appears to be loudest right at the fuel tank - almost as if it’s coming from the tank itself. After the engine stops, the noise winds down after about two seconds - as if a small motor of some sort is winding down. My thanks for any assistance.

Fuel pump. However, another gear head will have to tell you w/ more confidence whether it’s on it’s way out or not.

My opinion is that it could be normal, and the fuel pump has a long life ahead of it…(other owners of GM trucks similar issues?)

…or it is abnormal and is a sign of a doomed pump (likely)…

The fuel pump could whine like this for another 50 thousand miles before it dies (risky).

I fuel pump, could be noisey long before death…and full tanks quiet it down (diagnosing tip!)

And, from Click and Clack (excerpt):

Tom: Fuel pumps DO make noise when they’re starting to go bad. They make something between a whine and a groan. And if Goose has accurately diagnosed the fuel-pump noise then your fuel pump may be starting to go.

Ray: But I say tough! It’s possible for the fuel pump to start making noise before it’s gotten bad enough to affect the fuel pressure, and therefore the performance of the car. And if you’ve had the pressure checked recently, and it’s up to specifications, then I don’t think you’re obligated to fix it.

Tom: Goose is probably just trying to knock a couple of hundred bucks off the trade-in value of your car so he can make a bigger commission and get those sexy new plaid pants he’s had his eyes on.

Ray: If the pressure specification are good, then I’d just fill up the tank (the fuel pump is inside the gas tank, and it makes less noise when the tank is full) and trade it in. And if Goose doesn’t like it, tell him to go lay an egg

Definitely fuel pump; located in the tank on your truck. I don’t have enough experience to know whether the whine is normal or not; I can only note that my Omni has an electric fuel pump that has whined since Day One, 200K miles ago. Contrarily, Mrs R’s Toyota and Miata are both silent. Can you listen to other similar trucks?

I think that even though I’m very pro-zombie, this post should be spun off into it’s own thread. I reported it to let a mod make their own decision.

Moved the post to it’s own thread, closed the Zombie.

samclem Moderator