I have a 99 ls1 in a TransAm and when i start it up the lifters make noise for about 3 to 4 seconds. Oil and filter are new. Old oil was clean every time i have changed it. Car runs great and has about 40 psi oil press at idle hot. Got any ideas?

 

The noise is most likely piston slap. It is common and nothing to worry about.

 

noise goes away too fast to be piston slap. I've had that in other ls1s. Is something bleeding down over time?

 

Maybe there is piston slap after 3-4 seconds and you refuse to hear it. Maybe it starts out loud and it gets more quiet after 4 seconds. Get a video of it to so we can hear whats going on!!

 

Mine has terrible lifter noise at start up too, if i run it hard then its really bad the next time i start it. After a oil change it really rattles, I have 40+ oil pressure at idle hot, car runs ok. Its more of a rattle than a tap in mine, i actually think i'm hearing the rockers tap on the valves until the lifters pump up with oil completely. I also have the piston slap noise but that you can't miss, its a klacking knocking noise that goes away after it warms up.

If i drive it easy for a few 100 miles the noise goes away completely, then if i run it hard it comes back. I guess gm has some lifter issues.