I have the same exact whistle that has been driving me nuts for months. I have the PRM CAI. A couple of weeks ago I had Chiung take a drive in it and he knew exactly what it was. It's the CAI situation noted above. They all apparently do it to varying degrees. We even took a ride in his car and it did exactly the same thing with a different CAI. No problem just annoying. Not sure of the solution to get rid of it other than going back to stock or getting a better stereo!