my buddies truck sounds like the valves are rattling, what are they normally adjusted to? and how hard is it to adjust them? anything else it could be besides the valves?

 

Those rockers are torqued down to 25 foot pounds. Not adjustable. Probably not getting oil due to a clogged oil pump pickup screen.

 

Probably Valve Clatter, its actually called Detonation or Spark Knock.

Carbon on pistons, timing to far advanced, EGR components bad. There could be a lot of reasons for it. I had it on my 97 F250 5.8, I checked all the above and the only way I could get rid of it is to use 93 OCT gas ( Super unleaded ) I am thinking a P.O. might have put a chip in it but not sure.