Thank you for your service.
As Burla mentioned above, check for exhaust manifold bolts leaks - if none bolts are broken, then it could be something in the engine (in general terms without speculating too much). Your options would be to:
a). tear down the engine and start replacing thing such as lifters and cam ... just speculating here, but those are frequent issues in hemi's. This is probably not a great option if truck drives fine and CEL present.
b). Don't do anything - and wait to see if something may break eventually - if it does break, then most likely CEL will light up and give you a hint... then you can do the (a.) option.
c). option is to not do anything and just drive it... there's also a chance that it will be making all sorts of sounds/noises and will continue to run until 200k+ miles.
You can try Redline oil and see if that'll quiet it down... a cheap solution to make it quieter (can't guarantee that it'll solve all problems, but quieter engine isn't a bad thing). We run 5-30 Redline and royal purple filter. It doesn't help everyone though so not a silver bullet. My truck still has slight hemi tick.
good luck!