What's this pulsating sound?

[hheynow]

I've had my truck for four years and am familiar with every sound/noise that I hear...the injectors, the turbo, the tires on pavement and wind whistling through my old door seals. There is one sound/noise that I can't pinpoint. At a steady 65mph I hear a Wah...Wah...Wah at about one second intervals. It's a pulsating sound. I hear it at all my chip settings including stock. It seems like the rpms are pulsating but my tach is working fine and is steady as a rock. Any ideas? The truck drives flawlessly, but since I'm anal I'd like to know what is this sound/noise. BTW, it's been there way before I switched to B-100 so I ruled out biodiesel.

 

[rickh]

Drive shaft balancing? I had a slight noise in the CC and shimmed the carrier and that took care of it.
Assume with hubs unlocked?
With OD on or off or both.
A/C on or off?
Try and think of things that turn when you are moving, and if you can disablem them, try each one.
Check fan clutch side to side play.
Check water pump play.
Check pulley(s) play, remove serp belt to remove tension from them.
Rick H...

 

[hheynow]

Drive shaft balancing? I had a slight noise in the CC and shimmed the carrier and that took care of it. I had my driveshaft balanced last month when I got new U-joints Stupid question: Is the carrier the round plate between the transfer case and the front of the rear drive shaft?

Assume with hubs unlocked? Yes, unlocked

With OD on or off or both. OD is on at 65mph

A/C on or off? off

Try and think of things that turn when you are moving, and if you can disablem them, try each one.
Check fan clutch side to side play.
Check water pump play.
Check pulley(s) play, remove serp belt to remove tension from them.

I'll check those, but it sounds like it's coming from the engine.

 

[whatabudro]

If you have a long strait road (safe) around to then get up to that speed, put it in nutreal and kill the engine. That will cancel out alot of of possibilities.

 

[threejacks]

I have exactly the same noise. It's been going on for the last 4 or 5 months. My TC is very loud at idle and probably going out so I have assumed maybe this new noise was connected to the TC but I don't know. I know it has nothing to do with fan or belt as I removed them when I installed a new waterpump sometime before this new noise started.

 

[95_stroker]

Tires or wheel brgs.

 

[Crumm]

High or low spot on a tire would be my guess.

 

[hheynow]

I just checked my fan clutch. It's tight. The idler pulley (top pulley between the alternator and compressor) is a bit wobbly. Don't remember how tight it was before. Maybe that's what's causing the pulsations? Is it a PITA to change the bearings or easier to replace the pulley? What size bearings?

 

[threejacks]

High or low spot on a tire would be my guess.

I have put a new set of tires all the way around since this has started so that's not the problem. Same sound old tire vs. new tires.

The idler bearing is easy to install and can be bought at any parts store. Can't remember the number, but very common. Cost 2 or 3 dollars.

 

[3-StarJ.R.]

6203-2RS is the part number of the bearing.