A friend of mine has a '01 Silverado that has just started to make a loud and "oh so very not happy" RPM related tapping sound when the engine is cool/cold. Noise appeared to go away when the engine heated up, and to his backyard mechanic's ear, it sounded like a sticky lifter, loose valve lash or other valve train related problem.

As he had some other work to be done on his truck that required some professional expertise, he took the truck to a GM dealer workshop. He was totally not expecting the cause of the "valve train" noise to be driveline related, namely a cracked flex plate.

GM used to be notorious for blowing flex plates. I'd like to think they've changed, but maybe not. Certainly the newer flex plates are stronger than the older ones ... but the dealership found the problem mighty fast, so it may be a lot more common than people are aware of.

Another friend had a similar problem years ago on a '79 Monte Carlo. The car would shudder like HELL at speed, and at idle, you'd hear what sounded like valve chatter. Lo and behold, the flex plate was cracked and out of line, and that sent the torque converter wobbling like hell ... which killed the front main seal on the transmission.

hmmm.. thats odd. Since in my 01 before it got totaled it would have a slight ticking when cold. you could hear it well inside the truck. but when it warmed up it would go away. And I couple of guys from GM told me that the oil wasnt getting to the lifter over in the number 7 clyinder and it was normal. since during winter all 5.3 have a slight ticking when cold for about 5 minutes.

I didnt think it was a cracked flexplate tho. Since i would expect that to be more noticable.

The main reason you'd get a vibration with a cracked flexplate is because, just like the driveshaft, crankshaft, and more or less every other shaft on the ride is weighted to make it balanced. Toss a crack in there and you throw all the balance off. I haven't heard of this problem yet, and I know I'm just a lowly parts guy, but I figure that I would have heard about it by now.