Quote Originally Posted by atashashane View Post
This may be a leak or hole in the hose of the vacuum. When you increase the speed by pressing the accelerator pedal, the pressure rises in the pipes make a hissing sound. High pressure drops when you release, and the sound disappears. Have someone hold idling so you can locate the leak. In addition, many high intake air flow and some stock air intake make a whistling noise at high speed. This can be controlled with a little reving the engine while someone is listening to the air intake.

And also check the vent pipe of the PCV valve and PCV valve itself. It 'is blocked? you can look for some Audi repair for some guide about what to do with the whistle sounds..
The only problem with this is that whether I am giving it gas or idle the whistle is constant......meaning that no matter what is done the whistle is the same frequency and doesn't change with or without gas. So it makes it hard to locate it by having someone hold the gas to try and locate it.......I am going to check all the PCV valves this weekend when I have time if the whistle wasn't fixed today by what I did..........Also I have had the K&N filter in the car for the past 2 yrs so there is no reason it should have just started whistling within the last month......