4.8 engine rattle at start up

On cold engine start up I get a loud engine rattle that goes away in about 5-10 secs...hard to determine source...could it be the EGR valve?? or multiple lifters?? Benny

this will not help but

gm says a slight cold knock or piston slapping noise is considered normal if not present after the engine reaches normal operating temperatures.

well thats what they told my buddy he has a 5.7, this also happens on some 5.3's, and gm will not due anything about it.

how many miles are on it.

this will not help but

gm says a slight cold knock or piston slapping noise is considered normal if not present after the engine reaches normal operating temperatures.

well thats what they told my buddy he has a 5.7, this also happens on some 5.3's, and gm will not due anything about it.

how many miles are on it.
Howdy, I have about 76,000 miles on the truck, mostly hi-way...Used to get just a bit of lifter tap before but the last few days it`s been like a diesel on start up but clears up very quickly....About a week ago I changed from Pennzoil syn. to Mobil 1 syn. but can`t see that as the problem.unless the place doing the oil change changed the viscousity severly...Hmmm....Benny

do you know what types and viscosity
kind of odd started shortly after oil change
maybe penzoil was 5 or 10w-30 or 40 and the mobil 1 is a 0w-30 or 40 and lifters are draining down more than before