這裏是letter from VW,也沒有說具體原因，

VW's going to extend the warranty on all 1999-2001 2.0 Golfs, Jettas, and New Beetles. and 1999-2000 GTIs. For 10 years or 120,000 miles. Here's a jist of what it says. "Volkswagen has determined that under certain conditions, production deficiencies affecting the catalytic converter on your vehicle could make it susceptible to damage. If this happens, you may hear a readily recognizable rattling noise coming from under your vehicle in the area of the converter and the MIL light on the instrument cluster may illuminate. In some locales, an illuminated malfunction indicator light could cause your vehicle to fail a smog check program, and your vehicle registration application could be denied. Additionally, a malfunctiong catalytic converter may adversley affect teh driveability of your vehicle." VW will diagnose and replace the catalytic converter if necessary without charge as long as the vehicle remains within the time and mileage limits of the warranty extension. It only covers diagnosis and replacement of the catalytic converter only. VW will reimburse if you've had to replace your converter too. It's funny cause I've got the same problem with Elwood and I thought it was the mid muffler, so I guess Elwood's going to get a new cat and his Magnaflow exhaust. Hope this helps gang.