I'd like to buy a clue here. I had to replace the passenger up-pipe on a early 2004 build. The bellows were completely ruptured. I pulled the turbo out, went back with a solid up-pipe (egr deleted already). New bolts all around, new gasket between the up-pipe and y-pipe, and new v-clamps on the turbo. I put the exhaust bolts in loose, set the turbo in and had the y-pipe lined up (as far as I could tell) and put the clamp on and snugged it down. I put the down-pipe on the turbo, lined it up and snugged it down. Got the bolts in the turbo, and tightened things down everywhere. What little you can see of the y-pipe to turbo looks right. Cleaned the boots and put them back on. Fired it up, and everything sounds good, no extra noises. Took off, and at 8.5psi boost the moan starts, and it will change pitch and intensity all the way up to 19.5, which is as high as it will go (which kinda tells me I've got a leak somewhere). If the boost drops below 8.5, it quits making noise. I've put about 100 miles on it, and I can't find any soot anywhere on the exhaust side. All the boots seem to be on tight. I am going to replace the turbo to intercooler pipe boot, but I don't think its leaking. Anybody got any suggestions on where to start? Before I replaced the pipe, I had either a whistle (drove my wife nuts), or you could hear the air escaping from the bellows, never this. There's a file at so hopefully you can hear what I'm hearing.

 

If you can duplicate when in park, have someone push down on the exhaust pipe tip when it starts to moan. When mine moaned, I learned the exhaust vibration caused mine.

 

Sounds like you've got a bound exhaust with the work you just completed.

Here's a TSB for it. Most likely if you loosen the connections starting at the Y-pipe, realign, and retighten it will alleviate the issue.

6.0 Moan/Droan Between 1500-2000 RPM:





Engineering has investigated this condition and found the cause to be engine firing pulses causing the

turbo mounts to vibrate/resonate. For trucks built through 9-29-03 install a revised turbo pedestal, P/N

3C3Z-6N639-BA. Trucks built after 9-29-03, install a turbo bracket A-brace, P/N 5C3Z-6N639-BA. If

the draon is still present after installing the brace on trucks built from 9-30-03 through 1-17-05, replace

the turbo pedestal with 5C3Z-6N639-AA. Ensure the droan is not caused by a bound exhaust system.

Inspect for any damaged or broken exhaust hangers. Check the turbo downpipe by loosening the pipe at

the top and bottom, checking its alignment and retightening. If the droan is still present, check the part

number embossed on the turbo pedestal just below the turbo compressor outlet to the intercooler. If the

number IS NOT 1846207C1, replace the pedestal with the above part. After replacement, or if the

number IS 1846207C1, loosen the turbo inlet pipes and EGR cooler flange and neutralize by installing

the components in this order: snug the flange between the LH and RH inlet pipes; torque the EGR cooler

clamp to 53 in/lbs; torque the pedestal bolts to 23 ft/lbs; torque the turbo inlet clamp to 9 ft/lbs: snug the

inlet pipes to manifolds. Ensure all components are properly aligned. Torque the flange between the LH

and RH inlet pipes to 20 ft/lbs and the inlet pipes to the manifolds to 20 ft/lbs. Broadcast Message 0992,

SSM 17530, TSB #04-9-4 & 05-19-12.

 

I went and checked, it is not RPM related. It is definitely boost level related, and only starts at about 8.5psi. RPM makes no difference in the sound level at all. Also, I can't smell any exhaust fumes at the front or in the cab like I did before, so I'm seriously wondering about the boot at the turbo going to the intercooler pipe. I didn't really like the looks of it when I had it off, and I've got a new one ordered, should be here tomorrow. I did blow that boot loose once, and I think I had found a weak spot in it, so we'll see what happens with that.