I searched and can't seem to find the answer I'm looking for...If I replace the stock cat with a hi flow, do I still need the air pump to keep the hi flow cat "healthy" enough to work properly and pass emissions or does it flow enough that I no longer need the Air Pump?
My air pump is starting to make noise and I want to put on a hi flow rather than a mid pipe.

 

Yes even with a high flow cat, it is still a cat. You do need the air pump. If it's making a weird noise the bearings might be going inside, you might have to get another one. You can get a midpipe or gut your cat and get rid of the air pump or you can find a cheap used air pump in the parts for sale section Should cost you around 35-50 bucks for one used. Don't bother going to Mazda to get a new air pump, I belive they want somthing in the 1300 dollar range for that POS.