The Nissan Path

Like the title says, the error code is consistently coming up (tho i clear it) as P0420.
I ignored it for about 5 or 6 months now.
But about a month ago i started hearing the rattle - it is not a heat shield.
Had it up on a houst by a local mechanic and the rattle (hitting it by hand) is coming from the front driver catalytic converter - as if chuncks of metal or coins are loose in there.
But no rattle on the front passenger cat.
Should i replace both?

Just so you know about 3 years ago i replaced all 4 cats - they were super cheap!!!

I would replace both upstream converters if I were you. They may have been cheap, but they only lasted 3-years, so...? I've had good success with Walker Ultra converters from Rockauto; mine are 7-yrs old and still doing good. I deleted my rear converters with Doug Thorley mid-pipes. I would also not put the job off much longer. Being that the variable camshaft timing is used to accomplish EGR, it's possible that broken bits of catalyst substrate can be sucked up past the exhaust valve, into the combustion chamber, where it can score the cylinder walls and eventually create an oil burning engine.

Thanks SMJ,
I don't know how many lunches I owe you already

I was about to get supercheap ones (USD 150 for both front at premierautoexhaust) but I will go with walkers - I plan to keep this truck for at leeast 5 more years.

Thanks again!