Follow-Up:
I have 98 express van under ext. warranty that has a 2-4 min cold start knock . gm says this is normal unless it goes to 5 min they say it is not hurtng the motor. yeah right. there are other 5700 vortecs doing the same thing inc the mech at the dealership who HAD a 99 silverado which he said gm will do nothing for. I think a class action suit is in the works here,as I was told by gmac that my complaint is fairly common.chev cust relations told me they looked into this last sept 2000 and stated that the piston once to temp would reduce the noise. okay so why does it have make the noise in the first place? no ansewer, will it eventually become a 5 min knock after my warranty expires? again no ansewer. the warranty division will not authorize the repair which cheverolet says won't necessarily cure the problem. so you see how this works. gm knows they have a BIG PROBLEM here. funny thing here is that I have A FORD E 150 THAT HAS 270000 MILES AND HAS WORKED HARDER THAN THE CHEVY FOR 9 YRS AND STARTS UP WITHOUT A PISTON KNOCK. GM SHOULD CHANGE SLOGAN TO " LIKE A KNOCK ".