See my original thread "'01 to "02 Yukon Denali". Anyway, I brought my Denali in to have a Cold Sart diagnosis done on the vehicle and the service rep. just called me back this morning and told me that I do have a knocking sound. Possibly a piston problem. I suggest ALL yukon owners to get this diagnosis done ASAP BEFORE their regular warranty expires, unless you have an extended warranty. The person that I met who had this same problem got a brand spanking new engine from GMC.
You may ask yourself why wouldn't this be a recall? IMHO it would cost too much money for GMC. If only a handful of people found out about this problem it wouldn't cost as much as a TOTAL RECALL! I'll keep everyone updated on this forum.