It stays for a while until I give her some gas, any thoughts? It doesn't sound like a loose belt.

 

Sounds like your air pump. It starts up when cold to preheat the cats and lasts for about 10-30 seconds on cold startup. It probably turns off when you gas it a bit because you are heating the cats naturally and they no longer need "pre-heating". From what I understand it helps them reach operational temps sooner so you spit out dirty exhaust for as short as possible.

On both of my LS1's it was very loud and annoying. After I got headers I had it disconnected - no more whine...and no more cats! I don't know if disconnecting it with cats reduces their lifespan or not.

 

Thanks for the info.