I'd get under the car and check it over completely for holes... feel along the top of the pipe too. Also... not necessarily totally recommended... might want to get someone small and light inside your car while you lie underneath it (up on ramps of course unless you're REALLY skinny)... and start the car... should be able to tell really quick where the noise is coming from.
Of course, doing this when the car is cold is definitely a good thing... don't want any liability for burned flesh
And I agree with the earlier post... the Stebro exhaust pretty much rocks
