mine does this too, but not just at low revs mine does it when driving at all speeds more if im hard on the power even my dash lights dip for a split second its really irritating.
maybe a bad earth connection somewhere? ive had two rs200's and the first one was fine only a slightdip when turning to full lock when idling which i would expect since the clio's have electric power steering. im really not sure whats wrong with mine but there is definitely something so if you find anything please let me know