Knock, Knock

2001 gmc sierra 2500hd 6.0 litre. Cold driveway(5 - 10 sec.'s runtime) I begin to here a knock from the engine. This knock gets a little worse for about a minute, and then slowly goes away over the next 5 min.'s. My first thought was a wristpin. I guess it could be excessive valvetrain clearance due to cam wear also. Is this one familar to anyone ??? It is under GM certified used warranty, and therefore will be taken care of. Just interested if I'm "barking up the right tree".
Thanks, Bob.

Everyone i know has the knock. I am hearing it is a problem. GMC says they are looking into it.YEAH RIGHT. I am on a list.YEAHHH. Dealership told me it was just a common annoyance with GMC motors not to worry they say.

I am new to this forum but here is my two cents.
It Actually is the contact between the pistons and the cyl wall. Gm built these motors to have greater clearences between the two for fuel economy. There really is no Durability issue. But a little known secret is that if you contact the Customer Assistance Number for GMC/Chevrolet and ask for a componet letter ( and be insistant) they will get the local rep to give you a letter stating if that noise causes a problem they will fix it for upto 100,000 miles. I get them for people all the time. I have one. But dont tell anyone I said this because as a Chevrolet Service Manger I could get a nasty look from the Factory Bullies.