Long story short, with moving house and redecorating the whole thing, the Clio ended up going off the road for nearly two years awaiting a timing belt. Didn't really look at CS during that time either.
Anyway I got the timing belt changed last weekend - all running well again.
I happened to stumble upon this thread while doing the timing job, so in light of what
@Gibbo205 discovered I figured I might as well put on a new aux belt while I was there.
Fitted a new ContiTech belt this time (instead of Renault) and it only solved the bleddy thing didn't it! No more horse!
Inspected the smooth side of the Renault belt and it does have a subtle bump near where the writing is. Hadn't noticed that before as I'd only inspected the ribbed side!
Wild that little bump made it sound like a horse though. 😂
Cheers to Gibbo for reviving this thread. 👍