I have a 1997 Chevrolet pickup with 111,000 miles. I took it to repair the shop because of engine chatter when started in cold weather, valve lifter I thought. The mechanic checked it out and told me it was a warped piston head and it common in Chevrolet trucks,even in newer models,he told me to let it warm up for 5 minutes before driving. That has always been the case as the chatter ceases when then engine is warm. Do you believe that this is right? Also was told that is was OK for trips and not to worry about it.
I can’t tell you what’s causing the noise, but you’re wasting an awful lot of gasoline by allowing the engine to warm up for 5 minutes.
The engine will warm up more quickly by driving gently than it will by idling. I suggest allowing 10-15 seconds before driving off (except in very cold weather), but I can’t see how waiting 5 minutes is doing any good.
If the noise goes away when the engine warms up, you want it to warm up as quickly as possible, don’t you?
Are you sure he said warped piston head and not “piston slap”? You don;t say what engine you have, but GM had a problem with some engines wherein the piston skirts were apparently too short and were causing a rattling noise when cold by slapping against the cylinder walls.
Google “GM piston slap problem” and see if what you find fits your trucks symptoms. Post back.