Strange, had that happen to my 05 G35, but it shut off when I was on the interstate *shits pants*
It was a camshaft position sensor, bitch to replace too.
Yeah my wife's 2005 GT is loud but she has Flows and o/r X-Pipe and at the casino parking garage she sets off alarms. That setup is drone city but I don't mine that. If I get the Solo Race I will probably set the drone low or mid range :)
I have a feeling I will do this setup. I've had loud but not headers loud but my 2004 GT ran offroad x pipe with flows and it was raspy and loud when I let her open up.