Sounds like piston slap. How is your oil consumption?
If it is piston slap and you are getting it every day I'd notify your dealer of it and let them have it over night so they can hear it first thing in the cold morning.
I've read where it's noting to worry about, and I've read to the contrary.
I have only heard mine do it once about a year ago after leaving the car sit in the winter in a garage for roughly 3 weeks. It was loud, but witin a minute it disappeared and I haven't heard it since.
You can goggle up piston slap and read up on it. Here is one article you may find interesting. Read down in the article and there is a link where you can listen to piston slapping, it makes a tick tick tick sound.
GM Piston Slap -- Like a Knock
