My 02 S’crew with a 4R70W automatic, makes a sound like a spinning electric motor when it shifts from 2 to 3 and starting off in the morning. It has no loss of drivability. It pulls hard, doesn’t slip. It hasn’t popped a code, I had AAMCO check it out, they couldn’t find anything on an external diagnosis. The noise suddenly started last week. I had changed the transmission fluid approx 500 miles ago with Mercon V what came out looked great. There was nothing in the filter or any metal fragments in the magnet. The truck has 50900k miles of pretty easy, no towing, use. Do these have a weak point in the valve body or does anyone have experience with this?

 

I can't relate to your noise but to say often a hydraulic operating unit can develope a fluid flow generated noise like you often hear in heavy earth moving machines when operating control cylinders to work the machine functions.
This often is air trapped in the system at some point.
It can sound like a howl, a high pitched sound or anything in between until the flow route or pressure changes.
I had this in an 85 super cab with AOD but it never bother anything but me some times when the windows were down and going through road construction with barriers on both sides and close.

 

The best description,is when you take a ratchet with a socket, grab the socket and spin the ratchet like a noise maker, or like I said, a free spinning electric motor. Ironically, It stopped doing it as suddenly as it started. It would make the noise if I cycled off and on the the overdrive button and the 2-3 shift point it would do it. That makes me think a plunger was stuck in a bore in the valve body. I'm still concerned that this is a pre-curser to bad things coming. IE $$$.