The rattling may be due to the welds for the heatshield coming loose on the cat.
What brand sensor was used?
Was the ECU reset?
Here's some info from team-integra that may or may not be your problem.
The oxygen sensor measures the amount of oxygen present in the exhaust gas. Depending on the voltage generated by the oxygen sensor, the engine management system will change the air/fuel ratio to obtain the desired oxygen level present in the exhaust gas. A malfunctioning oxygen sensor sending an erroneous reading to the engine control system can cause a too rich or too lean condition. A rich condition will cause the converter to overheat and melt down from the unburned fuel being ignited while a lean condition can result in a misfire that can lead to the same result. Oxygen sensors wear out and need to be changed per your auto manufacturers time and mileage limits.