I had the "Tea Kettle" whistle until 2 days ago. I had checked vacuum lines, Throttle body. Intake gasket. Nothing seemed to be wrong. it would wistle at Idle and if you reved the engine while not in gear with no load on it. Put it in gear and drive and while your accelerating no whistle. Get up to speed and it came back, or let off the throttle and it came back. Drove me nuts. The wife could hear me pull in the driveway. Then I stumbled across the culprit. I have a 2004 with the 2 piece exaust manifold. The rear manifold has a collar on it with 2 studs that connect to a floating collar on the down pipe. The nuts that hold the floating collar along with the down pipe tight to the exaust manifold were missing. The collar was still in place but had no nuts forcing it together. As the engine warmed up exaust leaked out causing the wistle. Under load while accelerating the engine must have twisted just enough to form a good seal. Found 2 17 MM nuts in the garage and put them on. HOLY CRAP!!!! NO MORE WISTLE!!!! Peanut Butter Jelly Time!!! Peanut Butter Jelly Time!!! Peanut Butter Jelly Time!!!
Hope that helps some one.
If Peanut Butter Jelly Time leaves you scratching your head like my father. Here is a link. http://youtu.be/1TB6Xeye5-0
If you still don't get it, I am sorry I can't help you, please go to the lost and found and look for your sense of humor.