Alright guys, the whislte sound is natural. ITS SCIENCE!!! The whistle is the sound of the air and its velocity. Here's an experiment you can try at home:

1. Form your lips as if you are going to whistle
2. Now blow, and whistle
3. Keep your lips in the same position, but suck in air
Ah ha! So air can whislte when its being sucked in.

So the smallest change of path for the air being sucked into the car can affect the whistling. I have a generic short ram, and it doesn't whistle. But the slightest change in design or length can cause it to whistle.