I have a 2001 DeVille with a 6-year/100,000 mile warranty still in effect. When started the cold engine is very noisy and getting worse. It doesn't quiet down until at less two bars of engine temperature are achieved. The dealer says that is normal...a little bit of "piston slap" is not unusual. I have over fifty years of driving experience. The Cadillac shares the garage with a Volvo and a BMW. Not only is the Cadillac the nosiest in the garage, in my experience the only engines making this type of noise, be it "piston slap" or not, needed mechanical attention. Your advice will be appreciated.

this didnt belong in "Open letters"

Sounds like cold carbon rapping. Do a search for it here.

Yup, cold carbon rap. The fix is easy and fun. Drive it like you stole it. See Technical Archives at the top left of this page.