I have full Magnaflow cat back exhaust and tip, when you fire up the car it does have a loud gurgle that lasts for a few seconds. This is normal and just because of the RPM jump during start up. I cant tell you for sure if yours is normal as I would have to hear it for myself, because the Magnaflow exhaust is louder, you are able to hear it more over stock. It could of done it before but you just didnt notice because sound differance. I dont think its anything to worry about.