Generation IV Internal Engine - Lifter tick on truck

My dad came over to the house yesterday and as he was backing in, I could hear what sounded to me was a lifter tickin. He has a 2500HD, and he said that it's loud when it's cold and then goes away. Well my dad is kinda hard of hearing, and I told him that I could still hear it.
The engine is all stock, and is getting close to 100k on it. What would be the best plan of attack for him? I told him that we should pull the lifters out and check it out, but he's not really willing to do all of that. I told him that I would do it for him before something bad happens inside the motor.

Any thoughts guys?

Thanks in advance for the help

Are you sure it is a lifter and not an exhaust leak?? Check the back bolts on exhaust manifold on both sides and look to see if the bolt heads are broke off.