Diesel Bombers - 2012 with loud clank under load?

Hey guys, my parent-in-laws have a 2012 power stroke completely stock with less than 100k on it. They told me the other day that while accelerating there was a loud, almost valve tap sound coming from under the hood. They thought I'd know what it was bc I'm the mechanic of the family. My last 05 Duramax did the same thing every once in awhile. I never worried about it and let it ride, ran perfect when I traded it in years later. Anyone know what this noise is? Also the engine light is on, ran it with my scanner, results were 0 codes. So idk. If anyone can give me some insight or anything I would highly appreciate it so I can get that fixed for them. Thanks.