annnnnoying sound during rev idle at low gear

[Sardinas]

i have this very annoying sound during reving during idle or if the car runs 2t - 3t rpm na low gear na parang crack exhaust pipe ang tunog. sometimes lumalabas ung tunog minsan naman wala. my car is an SiR and is on stock exhaust. the sound is like this only that medyo minimal sakin kasi naka stock exhaust lang --> [ame="http://www.youtube.com/watch?v=Kqfq8eTr0Ng"]YouTube - Annoying Exhaust Sound (Fixed)[/ame]. i hope its not the engine but im pretty sure that its got to do something with the exhaust system or any loose bolts, supports, etc.

any ideas on what causes the problem? btw my car just came from a heavy bottomed and heavely damage my pipes underneath (na deform ung prang tubo (catalic ba un) at yong primary o resonator). i was wondering if d2 galing ung annoying sound.

[oj88]

The catalytic converter core may have been damaged/cracked and has become loose inside the exhaust system.