I have a 2007 GT w/BBK CAI and BBK throttle body, SLP loudmouths.No tune then.(Have one now).OK this started the other daywith a long run on the interstate. I noticed a rattle under the car. I thought it was the cats. It had thattypical broke-up cat rattle. I ordered a new Basani X w/high flow cats. Installed it -still rattles. Took SLP Loudmouths off and found all the welds on the inside of both mufflers broken. OK that would cause it to rattle. Re-installed stock mufflers w/ Basani X. Still rattles. Could I have burnt the valves or could it be valve rattle? Does it with or w/o the Brenspeed tune. I also have lost a lot of torque after installing the Basani X. It doesn't feel the same. No check engine lights, tach is steady as can be on idle. You can rev it up in the garage all day and not a rattle, only when your driving it. Before the Basani X it had great power but rattled, engine seems to run good. Reved up the motor with the hood up and it sounds great. Sounds like it could be coming from under the car. Can't figure it out. Wouldn't I see some signs from the motor if it were damaged.(Check engine,rough idle etc.)Please Help. I am considering returning everything to stock and take it to the dealer.(8500 miles). I am getting the guys that did all my custom mods to look at it tomorrow, they are pretty good.

 

To me it doesnt sound like an engine problem. Ive had rattles under pretty much all my cars before and its always ended up being loose bolts/rubbing exhast,etc. Hopefully someone with a S197 can chime in also. And the drop in torque is normal, by adding more exhaust flow you will usually loose some power down low but see big gains up top