Q: there was a rattle, which just disappeared but was replaced by a catalytic converter light.... can I still drive?

I can’t say with any assurance whether it’s OK to drive without hearing the rattle myself. It really could be anything and I’d need more information. But I’m going to guess that your catalytic converter is coming apart on the inside. That would explain your subsequent catalyst code. When the catalyst has been very hot, or maybe if you bottomed the exhaust on a speed bump, sometimes the ceramic substrate inside the catalytic converter will break up. And the pieces roll around inside the housing sounding like so many rocks in the exhaust. They can become wedged and stop rattling for periods of time, but will eventually start again. Sometimes the pieces can get wedged together and block the flow of exhaust to the point that the engine begins to run poorly. You need to have the ECU scanned for more codes, because if the catalyst did indeed break up at such a low mileage, there might be some other problem that caused the engine to run too rich and the exhaust to get too hot. I suggest you contact Your Mechanic about having a technician come to your home or office to hook up a scan tool and tell you what is bothering your car. They could also listen to your rattle and give you a first hand appraisal of whether it is safe to drive your car