Have a look at these two threads. They have youtube links to video demonstrating the sound in combination with G3 intake and ERZ HFC.:
Invidia Gemini CBE & ERZ HFC Review (with db comparison)
ERZ Performance High Flow Cats, Install and Review Thread
For my car, there's a tiny hint of rasp at around 3500 RPM heard from the outside, not in the cabin. I think this combination produces the best combination in terms of sound quality and minimal amount of rasp...you can read the impressions of the OPs of the above threads.