Check vac line to the fuel pressure regulator on the driver's side fuel rail. Unlikely, but, I had mine come off on a hard shift... engine was pinging... well, sounded like sheet metal ratteling it was so bad. Oops.
It sounds like you're running lean, and that CAI MIGHT be the problem. Put the stock intake back on and see if it goes away. If it does, then the CAI is the problem.