2004 Chevy Suburban 2500 with the 6.0L engine. It’s started this rattle at idle and under load at low RPMs. Idling it’s hit and miss, under load it’s steady. Moves up and down with RPMs. I was worried enough to cancel the trip to town. Is this a rod knock? Exhaust leak seems unlikely. Maybe lifters?
This engine has seen some abuse, uses a bit of oil. Good oil pressure, not overheating. Runs good otherwise and the noise goes away at driving speeds… Or at least I can’t hear it.
See the video. I run it some under torque lock (in gear with brakes on) and some in park. Definitely louder under load. The hit and miss aspect is what throws me off… Doesn’t seem like a rod knock would do that.
Chris it sounds engine external to me.
These have a trait of snapping off one or more engine exhaust manifold bolts with age.
Then a noise that comes and goes with exhaust manifold heat changes and engine torque twisting.
Listen up through the wheel wells. Louder?
Can happen at the same age, on both sides; confusing.
Yes; hard to do; but visually look for any missing bolt heads.
I would have said maybe an AFM camshaft lifter buggering up on you, if it had sounded engine internal. Heavier chassis 6.0L like my 3500 and the 4500’s did not use the variable cylinder systems . . .
Yours I am not sure.
Steve Unruh
It could be the exhaust manifold. I would check that first. If the oil pressure light is coming on, I might suspect a weak oil pump because of the whirring noise (which may be unrelated) or the clogged oil ports starving oil to the lifters.
The one tip below to help diagnose says use a stethoscope. You can use a small tube say 4ft long 1/4" tube and hold it -by- your ear (not too close or in your ear), to help determine where the sound is coming from.
This is what google aI pulled up.
Common 2004 6.0L Engine Noises
Lifter Tick/Tap: A loud, rapid clicking noise, especially on cold starts, often caused by poor oil flow or carbon buildup in the lifters. It usually goes away after a few minutes.
Piston Slap: A metallic knocking sound present only when the engine is cold and fades as the engine warms up. This is considered normal for many GM engines of this era.
Exhaust Manifold Leak: A ticking noise that sounds like a lifter but often persists or gets louder under acceleration. It is frequently caused by broken or rusted manifold bolts.
Engine Whine: A high-pitched, RPM-dependent whining, often caused by a failing fan clutch or power steering pump.
Fuel Injector Noise: A sharp, rapid clicking near the fuel rail, which is often considered normal operating sound.
Troubleshooting and Fixes
Check Oil: Ensure the oil level is correct and clean, as low or dirty oil is a primary cause of lifter tick.
Oil Additives: Using products like Sea Foam or adding a small amount of automatic transmission fluid (ATF) to the oil can help unstick stubborn lifters.
Listen to Location: Use a mechanic’s stethoscope to distinguish between top-end (valvetrain) and bottom-end (rod knock) noises.
Exhaust Inspection: Look for broken bolts on the exhaust manifolds, particularly at the rear of the engine.
Pull the valve covers and check all the valves are coming back up and seating. That dont sound good, I dont think thats not an exhuast leak. If there is bent valve it will rotate around and cause an intermitent sound like that. Eventually it will bust off and cause more damage.
Incredible difficult to diagnose sounds from a video but my 2 cents (ain’t worth nothing we don’t make Pennie’s anymore)
I can hear at least one if not two exhaust leaks, cheap the rear most manifold bolt they break off constantly on the ls motors the 6.0 more then others
I agree with Steve the knock sounds external, in day light hood open give the throttle a couple good wacks and watch the accessory drive the and watch for belt jump or idler chatter, the ac clutch and idlers were super common replacements. Worth pulling the belt off and repeating the test as well see if noise goes away
It has a lifter tick for sure as almost all ls do
Why I say it’s hard to diagnose from a video because I hear 3-4 separate sounds that indicate issues, non to major.
I am partial to the old school mechanics stethoscope for locating internal noises, available at almost any parts store and a tool worth its weight in gold for pinpointing engine noises
A poor man also can use just a chunk of heater hose, one end to your ear the other end searching for noise in and around where the eye balls cannot see, especially excellent at locating exhaust leaks
Non of that was probably helpful but that’s where I would start. Pinpoint the noise then investigate, while knowing the common issues
Also the 6.0 has a remote oil cooler then is always leaking at its feed lines from a gasket just above the oil filter, one of the beginning problems to causing premature lifter failure is running low oil pressure unnoticed due to the leak. Don’t trust the gauge on the dash it is not a true gauge it is a switch the numbers mean nothing to it it’s only reading if there is pressure or not
I’ll wrap this story up. I did end up swapping out the harmonic balancer. Some videos I watched sounded like the same noise as I was hearing, so I decided to go that route. Those are NOT easy to do on the LS platform without the proper puller and installer tools, so I managed to locate those and got the job done by day’s end. Fired it back up… and the noise was still there, no change. Very discouraging.
My conclusion then was, it really must be an exhaust leak. It did seem to be better after the car warmed up, which I chalked up to manifolds expanding and sealing the leak better. So went back to driving it and semi-ignoring the noise.
Monday, it got a lot worse, to the point where I pulled over again. I was worried the harmonic balancer had worked its way loose (you have to put insane torque on those bolts) but it was fine. So we drove home, and it was now making a rattle noise at all speeds, with or without throttle, just RPM dependent. I decided to let the mechanic have a crack at it, my time is just too limited to sink it all into this one project. Something was nagging me that exhaust leaks don’t act quite like that, but regardless I can’t have a constant noise like that, even an exhaust leak.
They called me just now, with the diagnosis. Flywheel is broken. It’s broken bad enough they don’t recommend driving it anywhere. $200 part plus $900 labor, which seems reasonable given they are pulling the transmission. I gave them the go-ahead, pulling transmissions is slightly beyond my ability at the moment, although I’ve done it before it’s worth letting them do it.
So thanks for your suggestions, I know it was a difficult diagnosis from a video and I’m not surprised nobody thought of the flywheel. It is a sort of “external” noise but it wasn’t coming from anywhere external. All that makes sense now. Plus it obviously has other exhaust leaks and noises to confuse things.
Any suggestions on other things they should do maintenance wise with the transmission pulled? I’m thinking oil seals etc. I did change the oil seal at the front when I pulled the harmonic balancer. I was just at the wrong end of the engine… Oh well. LOL.
Rebuild? Nah. I’m looking for little stuff that saves money because it’s already open.
I told them to replace the rear main seal, will take them no additional time with the trans pulled and flexplate already off. Gotta use the special tool of course, everything is a special tool now. I’m sure they have one.
You know I had an old Chevy K10 step side with a 350 and it had a broken fly wheel. Yup I was stumped for a long time before finding that and yeah I should have thought of that.
Yeah that a good feeling and bad feeling all in one. First its good because its not damage that cant be fixed like overhauling the engine or something. But the bad? yeah you have to unbolt the trany and move it back far enough so you can work on getting the fly wheel out. lol
