I have a 2000 Intrigue with the 3.5L and last winter it started to have odd noises. Early in the winter it started sounding like water when I accelerated, I thought maybe it was melted snow that was moving. That wasn't it.
Later in the winter it sounded a little like Ice Cubes flowing. This freaked me out that my coolant was freezing

. I checked the bottle that I had added with and it was frozen mixed 50/50 at 26 degrees. So I decided to switch to green coolant instead of dex-cool. Flushed 3-times with water and then used machine to flush in 6 gallons of green.
The water noise is still there in warm weather.