mine does that if I run cheap gas. Gotta run at least mid grade other wise mine pings. ALso on my old motor it pinged cause timing was off. Dunno if that relates though

 

It does have cheap gas in it right now. It sounds more like a tapping of a valve than an engine knocking from gas. Someone mentioned it might me a sticky valve due to carbon buildup and that it happens with Vortecs and wasn't something to worry about, but I don't know. They said use some GM top engine cleaner for it. I doesn't happen all the time and goes away so I don't think it is anything real major but I have been wrong before...

 

Hmmm. I've never been around the newer vortec fuel injected computer controlled trucks so I'm just guessing. Sounds like that could be a possibility. Run it hard for a little and see how it goes then.

 

Rick,

My dads 97 K2500 with the 5.7L did something similar when he was gone for 2 weeks. It was most likely that it was cold from just sitting there. And I had put cheap gas before he had left as well.

So what happened is when I turned it on after say a week of no use, I noticed a pinging and a bad vibration. But after that all was fine. It could just be that it was cold etc.

 

I was thinking that as well since it didn't do it this morning. I'll see what it does when I leave for lunch. I'll put better gas in it tonight probably and I'll check into the cleaner when I do my tune-up.

 

This happened to my brother-in-law on his 98 Burb. We used flushing oil on it twice and a can of Marvel in the oil, the tapping got better immeadiately and gradually went away completely over about a week.