Alright guys... I've got an unidentified noise going on for the last week or so. It's a chuffing noise at about half the rev rate... It sounds like a little 10HP single-cyl gas engine being run at the same RPM I am at, under heavy load.
This noise isn't apparent at idle, and becomes louder with more throttle. It's most apparent under load in the 1200-2200 range; it becomes drowned out above that.

I notice that the engine vibration is constant under that load(engine feels smooth); it doesn't seem to be losing power, running on 7 cyls or anything...

I'm thinking some sort of exhaust leak, but it seems like it would have to be right in front of one cyl for it to make that sort of noise, right?

It sounds like it's coming from the right hand side, but I checked that the exhaust manifold is in place, and the bolts are tight.

This noise started for me when I hauled a heavy load last Monday, I was pushing it - exhaust temps in 900-1050 range, running 2200-2600 RPMs mostly. Halfway into that trip, it became noticeable. Over the week since, it's changed, becoming more obvious and more "exhaust/engine like". At the beginning, it was kind of a "tinny" hiss, now it's more of a rumbling puff noise.

Thoughts? Where should I begin looking; what should I check?

 

I am a far cry from actually knowing much about these diesels, I have only had mine 8 months or so. But I recently had a "chuffing" noise myself, only when towing our trailer and a load of wood, uphill and against the wind, slowly... but when I pulled over it still ran great, couldn't tell a difference at all except the sound at idle up to about 1800 rpm. As my trip progressed it got louder but the same "sound" (not sure its what your describing) I called international and asked them and the guy said sounds kinda like a lifter was getting stuck or something similar, recommendation was to replace, or find a "old wives tale" method of adding a cleaner to the oil then changing it. All I did was change my oil, problem solved, no more chuffing of any kind. Maybe you'll be lucky like me. I also noticed when the hood was pooped the sound was most noticeable out of the air intake tube.

 

Chuffing noises are almost always related to improper valve opening in one way or another. My general guess at this would be a collapsed/stuck lifter.

 

you can use soapy water with engine cold start it and idle engine spray around exhaust manifold and look for bubbles, if you dont see any remove air intake filter and listen for a whooping sound , if you hear an odd sound your intake valves are not opening fully or are stuck from a lifter hanging up , I found a broken rocker and bridge once on a 6 liter that a customer brought for diag , pull your valve covers and bar your engine over and check valve lift on all cylinders if nothing is broken when you pull them

 

this is what i would do......

#1, pull off air cleaner (more difficult to hear with a turbo) listen for erratic noises.

#2, pull valve covers, rotate each cylinder so that the valves are closed
(lifters on the base lobe of the cam) and check for consistent "slop".

if you find a problem with a rocker, fix it and go to step #1.
if you still have a problem, change oil, and use any method of cleaner you desire.
diesel RX, ATF, or straight diesel. you do this at your own risk.
if you still hear the noise do a leak down test of the cylinders.

if your leak down shows that you have an issue, its time to get the heads done.
if your leak down shows as "set" i would be pulling the intake and changing lifters.

but IMO, if im breaking it down to the lifters, on a high mileage engine, head gaskets, studs, a valve job and guides i would be doing.
even went further and bought a new cam. with some expensive goodies to operate my valves

 

I would say lifter or sticking valve, every IDI 7.3 I have seen here in Europe the owners always mentioned it it happens time to time, I wonder why? Or is it old woman tale? I have read somewhere the clearances on the 7.3 were smaller to prevent oil combustion, but my sources are limited. I would remove the valve covers and inspect everything carefully.

 

So, time to pull the valve covers.
One thing to think about is it was recently rebuilt - 11K or so ago.
Here's a video:

 

Rob, check the exhaust leak first, seems to me there is an exhaust leak somewhere, manifolds, crosspipe, seems to me more like exhaust related. Do you have a muffler there? Isnt it clogged? I would check this before taking the valve covers off.

 

exactly what i was thinking. sounds just like mine with a cracked driver side manifold.

 

x3 on exhaust leak

 

As it turns out... Exhaust leak! My crossover pipe cracked right at the flange on the driver's side.
And by cracked, I mean /big/ crack. By the time I took it off last Saturday, the driver's side was completely detached; it came off in two pieces.
Surprisingly, I was still able to get 4 PSI of boost out of the turbo like that, but it was extremely loud whenever you hit the throttle.

I contacted Justin @ R&D and he happened to have the parts to make me a new one. So I'm now sporting the very first R&D Banks Crossover pipe!

Much quieter, and actually has power again! It's awesome. Now.... I just need more turbo. <_<

 

That's strange