i run a 2001 172 and have a tinny sound, almost rattly/vibrating coming from the centre exhaust somewhere. renault quoted me 275 quid to replace the centre section as they said there was a hairline crack near the cat. a second garage couldn t find any leak or crack . i ve been thinking about a slight upgrade to a better system . was just wondering if anyone else had experienced any similar problems or could recommend a decent system. cheers