2002 Chevy Suburban Engine Noise

I own a Chev 2002 Sub. 5.3 V8 4WD. The engine is making noises when I crank it up. Here is the scenario. Last fall at 73K miles, I took it to Chev dealer about a piston knock (sounded like one) when I crank it ( faint ) after about 30 sec. Of running. Oil Pressure was OK. I complained maybe I needed a motor. Dealer called GM Atlanta and they sent an engine guy to Montgomery to look at it. He said replace filter and oil pickup valve. He said that was 'normal' for that year model, that it would not hurt anything, as long as oil was changed properly. He really didn't give a good answer as to why it knocked AFTER the motor had been running for 30+ sec. And not at startup. Me being the dummy I accepted this right at the end of my extended warranty period. About a month ago, I noticed the noise getting louder along with new lifter noise. At 78K miles, now this is happening: Crank - lifters start making 'lifter noise' that goes away in about 10-15 seconds. After about 30-40 sec. Of being cranked, I hear the piston knock. It starts softly, then becomes very noticeable for about 15-20 sec. Then softly goes away. The noise is getting more pronounced the last month or so. I change the oil regularly at 2.5K-3K miles. No one at the dealer can explain it. If it was going to knock, I figured it would knock on startup, when the oil volume / pressure is at its lowest, not after the oil pressure / pumping is already running and appears normal. The motor runs softly after this and runs pretty smoothly. What to do? I don't want it to leave my family on the side of the road. I even used Slick 50 once to see if that would help. No diff.

Thanks
Bucrepus
Donating Member