2003 Altima rattles while driving

[jvmagic]

and today it failed the smog with a NO (ppm) reading of 876 (max is 437). The smog tech does not know why and he stated it may be a catalytic converter.
I had the service engine soon LED on for only a few minutes and reset it before I took it to get the smog but it did not help (the LED is not usually lit).

Any advice would be great.

Thanks in advance.

[PeaCe2DaGoD]

You know our cars the pre cats goes bad on the VQ35DE and the QR25DE, id say get that checked out. That usually goes bad before the Cat converter. Do you know what code the CEL was giving you? That can help out a lot also especially if it came back after a reset