I have a hearthrobe stem as well. I have slight leaks at the clamp area where the pipes join to the convertors. once it warms up the noise goes away.
You could try taking the clamps off and smearing high temperature silicone on the joints then reinstalling the clamps. have done this in the past on exhaust leaks and it worked.
2011 GT. Grabber Blue. Procharged. 3:73 manual.Billit LCA's. Corsa Extremes. GT 500 wheels. Racemaster DR's. T-56 Tremec. Dynotech DS . Centerforce DF. American Racing headers/high flow cats 560 rwhp.Donny Walsh tuned
2012 Pony Package. Race Red.3:31 automatic.BBK longtubes and catted X.FRPP Sport axlebacks. BBK throttle body. Dynotech DS. Brembo wheels and tires. Strut tower brace. Airraid CAI. Bama tuned.