I recently purchased a used 2002 Dodge Ram with 4.7L engine. It idles smooth and sounds fine under load but as you let your foot off the gas, around 2500 RPM, it starts making a diesel clattering noise. It's less about the RPM and more about having the engine at only a slight load. The engine is apparently a recent long block rebuild (only partially aware of what that means). The check engine light comes on with a P0420 code (upper catalytic converter sensor). I looked at the spark plugs and they looked nearly new. Changed the oil (which also looked good). Started running it on regular gas and then topped up (about half a tank) with premium and no difference in engine sound. Any ideas?

Here's a link to sound clips taken from various locations around the engine:

https://sites.google.com/site/2002dodgeram123/home

The 'Right Valve Cover (Driving)' sound clip demonstrates the noise very well. The noise can be heard in varying degrees in the other clips.

Any suggestions would be most appreciated!

 

sounds like a loose lifter