Weird Exhaust Sound
 

I have a SLP LMII catback system with a MAC O/R Prochamber. When the car is cold, I hear a sound that almost sounds like bb's rattling from what sounds like the left resonator (its not very loud, but I can still hear it from just the left tail pipe). After the car heats up, the sound goes away. But, it also makes a sound that sounds similar to if there were leaves caught inside the resonator when I turn the car off. The bb sound goes away after the car warms up, but I can't figure out what is making it. I haven't been able to pull the resonator off yet to look inside, but I am wondering if anybody has any ideas. It sounds fine when I'm driving around, it just makes the weird bb sound when I first start it up. I checked the clamps and they are all tight.

Ideas?