The exhaust clamp from the downpipe had rusted out and caused a blow. 7 quid part from Renault, jacked car up, fitted with exhaust paste as a precaution, and my god, transformed! Much nicer sound that I'd forgotten about (developed over time), plus the flat spot appears to have gone!
One warning though - the standard clamp allows only a tiny part of the thread to get the nut on - once you have it's easy to tighten up, but it's a right bugger to get it to that stage!
One warning though - the standard clamp allows only a tiny part of the thread to get the nut on - once you have it's easy to tighten up, but it's a right bugger to get it to that stage!