if he has a 2002 2500 it's still a 2nd gen

I'd do a full tuneup, going to colder plugs can help, higher octane fuel, as well as using a 180 thermostat as well I remember reading offhand too.

I've done a lot of reading over time on which plugs people like best, I'm actually using some right now without problems I NEVER hear about anybody using in these trucks, just regular AC DELCO copper plugs. Many love autolite copper ones. I swear I vaguely remember reading either platinum came stock on these trucks or the later 2nd gens, champions, but I could be wrong on the platinum part.

People acted like the world was going to end if people used platinum or double platinum or iridium plugs with the 2nd gen trucks but I drove around fine with some worn out double platinum's that the old owner had in(with some regular platinums oddly thrown in) and one so worn out I probably was running on 7 cylinders for awhile until I did a tuneup, the dist. cap and rotor were very corroded and the truck still started right up and drove fine around town and some highway driving and offhand got about the same mpg I do now LOL.

 

Stock plugs were plain ol' coppers. The reason we recommend against the rare earth plugs is, too many folks have had issues with them. Mystery misfires and such. Changing the plugs solved the problem. Sure, there are folks that can run them, and have no problems at all, but, for the most part, its better to stick with the copper plugs.

 

I was intrigued by these Denso Platinum "twin tips" at first but figured the claims of better fuel economy might have been inflated https://www.rockauto.com/en/moreinfo...095645&jsn=479

I was originally going to get some copper autolites, same heat range as stock, not those colder ones people recommend to fix pinging, but autozone happened to be out of stock of them

I read if you don't do a lot of long distance driving where the truck can really heat up colder range plugs can tend to foul/carbon up though, so there's that to consider. I mostly do a lot of in-town stop and go with a little highway mixed in so I figured stock heat range for me would be best

 

It's not ping then if it happens at cold start and when decelerating. At least not hot spot predetonation. Spark knock could happen with a bad plug, wire, old cap/rotor, etc. Or something is loose or even an exhaust leak can sound metallic. If you don't know the history, definitely do a full tune-up and see how it all looks. Get some injector cleaner like Techron for the tank, and run a treatment of seafoam. Get some baseline info to start eliminating the easy answers.

 

I think a few folks got on board with assuming you had pre-ignition because you used the word "ping" to describe the noise. "Ping" is a long used term to describe pre-ignition. It doesn't actually make a tonefull "ping" sound. "Engine Knock" or "Detonation" are other terms used to describe the same thing. Engine knock happens when the fuel/air mixture ignites earlier than it should either because the ignition timing is too advanced or, much more often, a combination of other things. All 2nd Gen Rams have their ignition timing set and controlled by the PCM and it is not adjustable.
Correct me if I'm wrong but I'm going to reword your description. The engine is making a metallic noise that is in sync with the engine revolutions. The faster the engine spins, the shorter the interval between noises. The noise is generally the same if accelerating or decelerating but is always dependent on engine speed for the number of noises per second.
To be honest, the problem could be any of a number of things and I like the idea of "Heat shield of loose exhaust". You need to determine whether the noise is internal to the engine (a bad thing) or external. It could be something loose outside of the engine, not likely but it could even be the A/C compressor, the power steering pump or the bracket that holds them on. Get into a warm quiet garage and spend some time just listening under the hood and under the truck. Do it with a buddy for more opinions and observations. More often than not, I've found noises attributed to the dumbest things. A mechanic's stethoscope isn't as far fetched an idea as it looks and it doesn't take an experienced grey skinned geezer to use one successfully.
What is your oil pressure gauge saying? Is it operating the same as it used to? After 30 minutes of operation, does the oil pressure still look good? If its convenient and near the time for an oil change, do it. Read any dodge truck manual you have and if there is an optional higher viscosity that you are recommended, use the higher viscosity oil. Listen to the engine before the oil change and then listen to the engine after the oil change. If the sound is different, you most likely have an internal problem. The most common problem is hydraulic lifters and they are on the lower scale of expense to address.
The key thing is to not make any assumptions or spend money and labor needlessly on guesses. 133K is still young for most truck engines so don't jump to any conclusions. My 5.2 V8 has 153K+ and it could still pass for a new engine from the standpoint of noise and oil consumption.

 

^ not a bad idea and good advice too. I have over 225k on my 95 ram and the engine runs and sound fine too. These engines are known to last a long time, 133k is really young for a 2nd gen ram. Has the truck been neglected like oil+maintenance? Hopefully it's nothing major.