If the converter is clogged up, the most common symptoms are low engine power, limited top speed (sometimes as low as 10mph), limited engine RPMs(often won’t rev beyond 2k to 3k rpm in neutral), and a check engine light for excessive EGR flow. Are you getting any of these symptoms? A sulfur smell can mean something has contaminated the catalytic converter, but not necessarily plugged it up, and the puffing sound may be a tuning problem or something normal that you have never noticed before, if it’s at the tailpipe. If the noise is under the car, you have a leak somewhere.