So I've been hunting down this issue ever since I've owned my 04 3.9 (140k). cannot understand for the likfe of me why it sounds like this, but there's an insanely annoying resonance coming from the throttlebody. It happens on cold starts, especially when the AC is turned on, and randomly during normal driving (usually when the compressor cycles) at first I thought it was the AC, but after a new compressor and removing the belt and running it i found that to be false (a+ troubleshooting skills). The sound is coming from my cold air intake. When I remove the intake and run the car just open throttle body it gets WAY louder. Like Darth Vader is creeping up behind you. No whistle. No vacuum leak (that I know of. Idles ok) no cel. I'm lost. And annoyed. I really don't think it's a huge problem. But you get the kinda looks in the parking lot like you do with a squeaky belt. I'm 98% sure it's something to do with the throttlebody. I replaced the iac with little results. Cleaned tb, nothing. Scoured the forums and haven't found much other than some BMW guys with the same problem. Help? Here's a YouTube link
View: https://youtu.be/57a-ey4OOcw