I have an '05 F150 FX/4 with a 5.4L. and Auto trans. The only add-ons are a Gryphon tuner with mild tunes, Spectre intake, and e-fans.
Lately while driving the truck I will hear a noise from about the back of the trans that sounds like a combination of air escaping or change rattling. This will usually happen between 3rd & 4th, but goes away when o/d kicks in. I can also hear it in those gears under hard acceleration.
I had a filter change & fluid flush about 15k miles ago. This truck has about 150k on it and never had any issues other than an IWE problem which I solved by replacing both accuators and the solonoid.
Anyone wanna take a shot at it?

 

I'm shocked!!!!! Has no one ever had this problem before???????

 

My bad! Upon closer inspection, it's another IWE issue. I've never seen or heard of the IWE noise showing up in only the downshift when you're already moving and speed up