Well it was meant to be a joke, but now that I think of it, one of my buddies had a dead mouse in his airbox on his intake. He came to discover it when he installed his CAI. I guess it would be possible that a mouse could climb in the pipe, but I think it would get really smelly, especially with the exhaust heat, so I'm guessing there isn't a mouse, but I hope you find out whats wrong cause that sound was funky.