Knocking at start up ?????

I have a 97 K1500 with a 350 vortec engine. When it sits overnight and I start it in the morning everything sounds great. When it sits for about 15 min or 30 mins it knocks for a few seconds at start up. What can it be?

about how many seconds? about 30 to 45 seconds. if so main bearings, it happened on my truck there is a bullettin on the GM Vortecs about it I can't remember were it is. The guy that rebuilt my engine found it on a disk about it. I beleive the crank was not torqued even. It usaully happens at about 80000 to 100000 miles.

Actually, it only for about 1 to 2 seconds, then it just goes away.

Sounds like its not oiling proper then if it does it after it just sets for a few minutes compared to not doing it over night.

what kind of oil filter do you have on it. it needs a filter with a check valve. ac delco or fram tough gaurd

Actually, I just got the truck so I don't know what type of filter is has. I'll be changing the oil this weekend, perhaps the filter it has doesn't have a check valve. I do know that it's not an ac delco or fram filter so that might be it.

Thanks, I'll let you guys know the outcome.

Homerun