I replaced with an aftermarket convertor but car is a bit noisy at acceleration..

You should get that shield and install it and put the OEM converter back in.
Aftermarket converters are very cheap.

 

Often, aftermarket converter assemblies and gaskets are not installed completely correct. Seen it many times where the fasteners at the exhaust manifold flange are not centered and it creates leaks. usually, it's all about attention to detail. The quality of the gasket makes a significant difference also.

 

no codes no problem

 

Replace the intake gasket with a new OEM one and new compression springs. The universal ones that come with the catalytic converter are junk.

 

Last aftermarket converter a customer used kept throwing CEL due to the volume being literally to small to process and catalyze the engine emissions... Go OE or OEM unless you're sure or there's a written guarantee.

 

Looks like he had and made an insurance claim on the first stolen one.

For most of us who live on a limited income and do not have a spare $2500 or $3000 laying around for a new OEM cat, the only option is comprehensive insurance only if we have it or a less expensive aftermarket cat.

The OP's got either a bad cat or a leak somewhere in the exhaust.

A good aftermarket cat should function well. I'd get a Walker or for more money, a Magnaflow.

 

I've replaced dozens of OEM Gen 2 catalytic converters in the last couple years, using the model I've posted about in previous threads (<$150). Always installed a new Denso O2 sensor from Rock Auto ($57) if the OEM was gone. As of yesterday, not a single one has triggered a CEL.