What causes small amounts of smoke to come from my exhaust pipe, even when its really warm outside?

I have a 97 Buick Regal LS 3800 series engine v6...a couple days ago I noticed after I start my car up and accelerate then put it back in park a little amount of smoke comes from the exhaust pipe, but goes away completely after I start driving for a few minutes....even on real warm days tho, theres no smoke when I start it up just after i accelerate a bit then put it back in park and go around to my exhaust pipe i can see little smoke comin out what may be causing this should i worry?????