My Z3 had an exhaust rattle at low speeds, which was diagnosed as coming from the catalytic converter. The only option I have here in Australia is to weld a new universal cat to replace the original unit as genuine catalytic converters are not available with BMW. I ordered a direct replacement cat on eBay manufactured by EEC in the UK and it arrived in Sydney within 5 days. Last weekend I replaced the catalytic converter and the following photograph shows a comparison between the two. The EEC cat (eurocats) is smaller than the original and shape of the inlet pipe is different. Apart from these changes, it appears to be good quality and fitted very well. The exhaust rattle has gone but the beat has slightly changed. I would like to hear from other members who have installed replacement catalytic converters.