Catalytic Converter C.E.L.

Wanting to confirm some advice I got from the dealer the other day. My C.E.L. came on intermittantly for the Catalytic Converter being bad. Additionally, I am hearing more of a "go kart" sound on heavy acceleration. The dealer told me that both are caused by a loose/ill fitted air filter. Ironically, the noise started after my last oil/air filter change, and double ironically the air filter was very challenging to seat properly. It was a FRAM. I will be going down to try to adjust that later today to see what I can see.

The dealership explanation was that the loose air filter could cause a poor mixture by allowing too much air in or directly make the noise through vibration. Similarly, the bad mix would get down to the CAT and set off it's sensor, like it is not remixing the unburned gasses correctly. Is this dealer taking me for a ride, or does this sound valid?

Will post an update after my next long drive with the air filter seated properly. Just wondering what y'all think?