Engine Knock

I have a 2001 GMC Jimmy, that when I cold start the engine I get an engine knock for about 5-10 minutes and then it goes away. This happened before about 6 months ago and I took it to the dealer, they said that is was problably a sticky lifter. They tried an engine flush which made it go away. Now it is back, worse than before. It has 65,000 miles and is not under and warranty anymore. Any information would be great. Thank you.

piston slap or the dealer says it is carbon buildup perfectly normal for a new gm vehicle

Well, I went to lunch and the was lots of oil pressure and all the oil poured out, I guess the rear main seal.

what now, let us know what you did next?? And, how much $$... I am looking to replace the CPI unit and internal lines on the intake...it is always good to know what to do when...