2000 chevy impala ls -

You may have a lower intake manifold gasket leak (or a head gasket leak-slightly less probable) the lower intake can leak onto the serpentine belt and fling oil (and/or antifreeze). The lower intake manifold gasket is usually the culprit here. There is much information about changing it if you are inclined to do it yourself. If not, expect around 800 to 1200 to fix at dealer/mechanic. This is usually accompanied by (but not always) oil in the antifreeze, or antifreeze in the oil...