Need help with tinging sound from under the Celi

[bickley]

Hey guys and gals, I have a strange problem...after driving around for a little bit, you can hear a loud "ting ting ting" sound from under the car. It sounds like it's coming from the exhaust system somewhere. I car hear it when the car is on and you can really hear it when you shut her off. Anyone know what might cause this? Thanks for any help u can provide. Oh yeah, I have a dual exhaust welded from the cat back.

Thanks