Shaking at Stops

[jasolhe]

2009 Pontiac Vibe 2.4 L
*only shakes at stop signs and stop lights, as soon as brakes are released and i hit the gas the shake goes away
*doesn't shake in park or while driving

I was getting both these codes: P0420 & P0301

I replaced Upstream and Downstream O2 Sensors and the gas cap, cleared codes with my bluetooth reader i bought and P0420 came back.

Should I just swap the Exhaust Manifold Catalytic Converter next? It has 190,000 miles? I only found 1 part online with 1 review so that seems odd to me. This one:

A-Premium Exhaust Manifold Catalytic Converter Kit Direct-Fit Compatible with Toyota Corolla 2009-2011, Matrix 2009-2013 & Scion tC 2007-2010 & Pontiac Vibe 2009-2010, EPA Compliant

Do you think an old/bad Exhaust Manifold Catalytic Converter would cause my shaking based on my specific situation mentioned above?

[jasolhe]

Forgot to mention. I bought this 3 weeks ago. The owner let me know the engine light had just came on and the shop read the codes and replaced the spark plugs and ignition coil #4 to address this.

This is driven rarely by us and the codes, maybe the ones I'm getting are new ones that showed up maybe not. I don't have their readings their shop pulled. Either way what they did was a plus I guess

[jasolhe]

Last thing on sounds that may be other things but I may as well mention it:

I get a whirring, air blowing whistling sound taking off from stop in the first 10 mph
I get a noise underneath the middle of the car "almost" not always exclusively going up inclines in the 35 to 40 mph range and virtually never at any other time, the noise is kind of a rattling type sound

Thanks for any suggestions anyone has!