Having had this problem on my own valver, including rumbling round slight corners, and its not always the rack. Track rod ends often get blamed and replaced with no change. Before changing the rack, check the inner track arm joint, under the gaitor on rack end. These can wear, and it is often diagnosed as rack, or track rod ends, when it is these. They are about £56 (well drivers one is) from Renault (my dealer says the are a known problem) and are a c£@t to change. The nut that holds them on is a ratchet type, and is destroyed on removal. This makes it hard to move and given that you pull against the rack when loosening it, its a bit scary, as bugger it and youll need a new rack anyway. Check them by jacking one side up, and reaching in push/pull track arm, whist looking at inner joint (play is really noticable if you undo track end from hub unit first). I got my dealer to do it as I was a bit scared to pull too hard against rack, half hoped they would burst the rack, so I could get one for free, but it came off ok. Difference in car was unbelievable, felt like a new cars steering again (apart from obligatory valver steering pump whines), this help anybody?