I've had this get worse over the past week. It sounds when driving over 20th and you hear what seems to be polystyrene rubbing against polystyrene. It's a mental horribly irritating noise. Going to remove my door card on Saturday to inspect. I think it's the middle of the doors. Worse my side but it's savage!

Any ideas? 

Check the trim on the bottom of the outside of the door. It might have become loose, give it a little tug to check.
If it's that you might get away with giving it a thump back in place, failing that you will need to remove the whole trim to replace the broken clips.
Buy genuine clips, the after market cheap clips are a waste of time.
Let us know how you get on.

No trim all tight. I'd installed steps about 4 months back wonder if the bracket is an issue now I'm thinking about it.