It's pretty common for the valves to loosen up over time with the pressure of the exhaust. There should be something at the top of valve flap that lets you tighten it, my corsa active has a allen head bolt.I have the Roush quad tip active exhaust on my 15 GT and one of the valve rattles when closed. I have had the exhaust for 6 years and just started doing this. Is there a way to tighten the valve?