1998 K2500 5.7L engine noise under load

First, thanks for a helpful forum. I've been a lurker for the last 4 months while I installed a rebuilt engine in the above truck (my first engine pull/replace). It has 230,000 miles, and 3 years ago it threw a couple pistons. Sat in the pasture until this past November when I had the funds for a new engine and other parts. Finished at the end of November.

Still taking care of small non-engine related issues (brakes, tailgate, windows etc) as time allows, but last week coming home in some deep snow the engine developed a very annoying noise. It at least seemed like a suddenly developed noise, and I can only hear it in the cab when under load. Idling, or running down the highway at 2200rpm doesn't matter, as long as we are going down hill. Any acceleration, or work, will cause the noise. Placing the foot firmly on the brake in gear while stopped and giving it gas will cause the noise. I have not noticed any change in performance.

It sounds like it is coming from under the hood, and to me it sounds like the sound playing cards in a bike spokes when I was a kid made. The higher the rpm, the faster the sound.

Now, I've adjusted the valves (they all seemed a little loose, and all tightened I would say 1/2-1 turn) but it didn't make a difference. Also, changed the oil (no problems with oil, but it was time). I also unplugged EVAP (evaporative canister) solenoid , but it didn't make a difference.

I did notice awhile back that I had grainy carbon deposits on a few spark plugs (yes, new like many other parts, just a few thousand miles on them). In my research, someone had suggested carbon build up would cause an engine noise, but the triggers were different and I wouldn't know how to clean that out short of tearing it down to the headers.

Ok, any ideas on how to track this down or what it might be? I appreciate any suggestions you might have!

Thanks,
Deron

One minor update. I was able to reproduce the sound while in neutral while bring up the rpm. By giving it a little gas from idle I could hear a fainter version of the sound until it reached a stead rpm. Still a load I suppose trying to bring the crankshaft up to a new RPM.

So, if no one has any suggestions, maybe someone has an idea on how I might check for carbon buildup and better yet how I might clean without taking the headers off etal. Maybe pump some liquid into the spark plug hole, or top a small hose to the end of my shop vac and stick it into the spark plug hole, or??

Maybe I don't have the valves tight enough? Anyone with practical experience setting the valve nuts? Generally speaking, when at #1 TDC, 1/2 of the rockers were loose (#1 I/E, etc). I tightened them up a few degrees and they started binding up when I turned them with my thumb and forefinger. I then tightened another 3/4 of a turn. This was per my Haynes. It seemed that it took very little tightening to go from loose to binding to unmovable. Less than 1/8 of a turn. Sound about right?

Since it is an under load issue, I'm also thinking that pulling plugs one at a time might identify it is a single cylinder problem, I'm just not sure if I would still be able to hear over the extra noise.

Just looking for a little advice,

Deron

One more bit of information. I managed to get a recording from inside my cab, and maybe this will be the ticket to get someone to recognize the cause. I posted the mp3 file on my site at http://www.faroutliving.com/enginenoise.mp3

I hope it is not a problem to reference files off this site. If some other information would be helpful, please ask.

Deron

Exhaust leak?
Check the gasket between the exhaust manifold and the engine (both sides).
Also check the gasket between the head pipe and the exhaust manifold.

The same applies if you are running headers, but instead of checking the head pipe gasket, you'll check the collector gasket.

Good luck!

Thank you quick69gto! Work is in the way of important stuff like wrenches, but I have been able to verify that there is indeed an exhaust leak on the bottom rear of the left side manifold. I was hoping to get it fixed and post the results at the same time so I knew for sure that was the problem, but it may be yet another week before time allows! Still, at least one more problem identified! Just a dozen more to go :-)

Thanks again,

Deron