Where Is My Fuel Pump And What Does It Sound Like Broken

[tomseeley]

I'm driving a 2002 2500HD dmax with almost 100K on it. Runs fine, as near as I can tell (diesel truck newbie here). But lately I've heard a distinct rhythmic sound coming from the rear of the truck and I'm at least curious what it could be. I'm almost certain it's more prominent in cold engine conditions rather than warmed up, but I could be wrong. It's clearly distinct from routine engine noise. I'm almost positive it is NOT road noise, such as from a tire with bad wear pattern or tread, or a wheel out of balance. But it sounds distinctly man-made, with an even but definitely speed-dependent sound. It's more prominent when moving than at rest and idling, when it's almost non-existent. Performance and mileage, etc., don't seem out of whack.

 

I'm wondering if the fuel pump is actually located behind the cab, for example, and maybe that's headed for failure? Or some other rotating piece of machinery back there somewhere?

 

I'm definitely not tech-savvy enough to have a clue to what it could be, but it's due for its 100K service soon and I'd like to be prepared to give my dealer an idea what to look for, beyond "I hear this noise; I wonder what it could be; maybe you could help me". As we all know, that's code for opening my wallet and inviting him to help himself!

[Draenor]

Is it a whining noise? If it is and it varies with speed, my guess is the differential. It would sound like kind of like the transmission of a small car backing up quickly. Thats the best I could describe it.