I can believe that. My '97 3.1 has rattled when started cold since new. I never really worried about it, cuz all the others I'd been around in the shop did too. I could have had the teflon skirt pistons put in when it was under warranty, but as a mechanic I know it is just asking for trouble to dismantle a new engine just to correct a harmless noise.
I have 117,000 trouble-free miles on this car, and I drive it like I stole it daily. It always sounds like hell first thing in the morning, worse the colder it is outside, but I always give it 2-3 mins of idle warm up after the first start of the day in cold weather, and it sounds the same today as it did when I bought it eight years ago.
What I hear is actually valve train noise, kind of clattery random light clicking, and occaisionally if it is real cold out and I have the door open when I start it, I hear the unmistakeable notorius piston slap that these are prone to. Not as deep or alarming as a bearing knock, but more substantial than lifter noise. But that goes away within 15 seconds or so.
I worked in a shop when these engines first came out, and they've always been noisy critters. But their durability is unmatched except for maybe the 3.8 Buick motor, that's why I bought it.