Off the grid groove.
Keep in mind; polyrhythms will at some point line-up with the major down beat of the time signature the song is in. After that happens, listen and see if the two voices which make the possible polyrhythm share the same fundamental beat or not.
If it sounds like one voice is every 4 beats, and the other is every 2 beats, they share the same fundamental root pulse. If not… then you might just have yourself something a little more interesting!