I love the whistle produced when I step on the pedal, it sounds like a jet talking off. But it gets too loud when my fresh-air vent door is open. Where's the sound coming from?
1. Is it the sound of air pushed from the intercooler to the intake horn?
2. Is it the exhaust from the turbo to the down pipe?
3. Is it the air getting sucked through the BHAF into the turbo?
4. Other?

 

I'd bet it's just the turbo singing. You can hear most of those from anywhere in or around the truck.

 

U mean the bearings in the turbo?

 

No, just the high pitched whistle coming from the blades of the compressor wheel. It's common to hear a whistle from most turbos.

 

And the compressor pumps air into the intercooler, right?

There's also a fan with blades in the exhaust housing, does that produce a whistling sound too?

 

Yep. Air is drawn in by the compressor and then pushed through the intercooler, then the intake.