You can hear it best on the video 18 sec to 22 seconds into the video it sounds like a hummm but like a soft grinding noise as well and it is defiantly when slightly excellerating between 60 and 80km.

 

Got it.

It doesn't sound consistent enough to be drivetrain, sounds like something humming with the wind and minor gusts.

This. I would also check under and around the chassis, make sure you don't have any plastic bags or other crap hanging on for a ride.

 

I don't hear anything but wind and buffetting on the clip either.

I've got one though (no video/audio yet) that I think I've nailed but I'll throw it out there.

When accelerating I hear a mid-pitch buzzing, almost like a small horn going off. It is short lived and increases then decreases in volume over the couple of seconds it occurs. The colder it is, the more often it occurs and the lower speed it happens at.

The first time I heard it I was accelerating onto the highway in mid-autumn, this morning at -20C it happened three or four times as the engine warmed up. Doesn't seem to happen warm.

I don't know for sure if these trucks have them, but it sounds to me like the air valve that diverts warm air into the intake is opening/closing and causing a resonance in the intake system.

Thoughts?

 

Fan clutch? Fan bearing? (Do they have one?)

 

Yep have that noise only when it’s cold or cool like for the first ten miles then seems to go away. Only when I push the gas pedal a slight bit and when I let off. Only under load. Will not make the noise in neutral and stepping on the gas. I have no idea what it is yet. Just started doing it at about 90k

 

That sounds almost exactly like the problem I was having. Same symptoms, and was more pronounced while the a/c compressor was engaged during idle in Drive. It turned out to be the serpentine tensioner, and the bushing between the floating piece and the fixed piece appeared to have worn down to the point where they were metal on metal during the above conditions.

Watch your tensioner when it's making the noise, and it will visually vibrate to the exact noise pattern if yours is the problem. It's a simple one bolt out, one bolt in job after removing the belt, just beware shearing the head if it's in there good. (I did)

 

I hope that isn't the case with mine! It only has 72k km on it! And I can't watch the tensioner when it is making noise, I'm doing 100km/hr!

 

Mine started very slightly at about 50-55k miles. It developed slightly worse over time to the point where I should start looking into it, finally was able to diagnose the problem and fix it a few months ago at about 66k miles.

It wasn't so much a buzzing than a mild "grinding", and only while the engine was under a very light load...such as when at a stop in Drive or "tapping" the throttle while in Neutral/Park (I didn't notice it while completely off the throttle in Neutral/Park). Engagement of the a/c compressor seemed to amplify it (this changes the load on the tensioner), and at first I misdiagnosed it as a failing compressor clutch until the tensioner vibrating to the noise pattern caught my eye. I can tell you it wasn't doing it under acceleration, or any other time the engine naturally "vibrates" less like while at speed.

Not sure what yours might be, but graythang's sounds much more like my tensioner problem.

 

Wow never thought about the belt tensioner. But why is the noise only in drive under slight load of light acceleration and not under load say while in park or neutral. Isn't the load the same to the belt tensioner in drive or natural?

 

Well I had my brother sit in the back seat to see if he could hear it coming from somewhere and he believes it is coming from the driver side just between the cab and the rear wheel. So I rolled underneath and the only thing that is there look like my e brake cable hmmm possibly could be the problem I'm going to try and rap some foam around it go for a drive and see if it helps.

Thank you for all your responses it really helps