Truck has 185k miles. It has had the tell-tell ticking since about 60k. Got progressively louder. Regular oil changes at 3-5k with 5-20 full synthetic. At 170k changed phasers, timing chains, lower gear, guides, oil pump, rockers, lash adjusters, and water pump. Ran quiet, strong, better than new. Was so excited, I bought a new Flowmaster exhaust, including stainless cats. Ran like a scalded dog. About two weeks ago, i noticed a ticking that sounded like an exhaust leak. I figured the connection between the new flared pipe and one of the exhaust manifolds had worked it's way loose. Over the course of a week, the noise has gotten so loud that it sounds like a diesel. Still sounds like a loud exhaust leak rather than a knocking from the phasers. Raised the vehicle and tightened the flange nuts on both sides. Still there. Started the truck and got underneath. No leak. No leak at either of the exhaust gaskets. Upon further investigation and took it to the muffler guy down the road, the noise is internal and seems to be coming from the intake, on top of the engine. Truck still runs great, pulls hard, idles like a caddy, no light and no codes. Thinking that it might be a bad rocker or cam that might be holding an exhaust valve open or not allowing intake valve/s to close during exhaust stroke. Took valve covers off and no visible bad rockers. Chains are tight, no blueing from heat, oil looks bfn. Any thoughts?

 

how about the EGR / tube system ?

 

I know it doesn't make sense, but loose spark plug? How about something concerning EGR?

 

first thing i thought of was loose spark plug as well. You'll know its that by just taking off the boots and if its wet the plug is loose.

 

double post

 

Thanks 1sax and Stang. That makes sense and would have been a simple and awesome fix. I would have felt like an idiot for taking everything apart without checking the plugs but it would have been worth the humility if that was the fix. After your posts, I checked the plugs, all are tight. I still have the valve covers off. Is there anything else I could look for? Thanks

 

With the valve covers off, I did find that one of the tabs on the passenger side cam phaser was bent toward the firewall. Not sure if the tab was bent when new phaser was installed or possibly when the valve cover was removed. Truck ran better than new when new phaser was installed and no code so I don't think it was during installation. What could have bent tab under normal engine use?