518 in a 92 Dakota, 1500 miles on a complete overhaul 100% stock, no shift kit, fresh reman T converter.
It whines like an old Powerglide, just started this today. Park/Neutral it whines, goes away in gear. Never heard such a whine like this, from a RWD Dodge trans of any kind, and I have been around a bunch of them. was quiet for 1st 1450 miles of it being in truck. ATF+4 fluid, was at "add" mark, added 1/2 qt to full mark, no change. Shifts fine.

What gives?

I have no magic idea but a suggestion or two. Drop the pan and see if there is anything in the filter that should not be there. Also are you sure it is the transmission? Is there a RPM sensitive accessory that could be making the noise?

Maybe talk to whoever rebuilt the transmission first and get their suggestions.

I rebuilt it not my 1st.
I did put a transgo kit into it, that didn't work out right. So I swapped out the valve body with the one that came from the trans that I pulled out, and solved that problem. (Weird, the last couple of these that I have overhauled and put the same shift kit into came out awesome.)
This trans was a spare that I had collecting dust, came from a 93 Dakota that I had swapped over to a stick.
It is worst in park reverse. Goes away in drive.

I did pull the serpentine belt and it definitely isn't anything driven by that. W/o the noise of the fan I could tell that it's not in the engine either,it is in the bell housing area.

The whining is usually caused by a rapidly cycling pressure regulator valve; more of an annoyance than a real problem. The factory recommended fix is to replace the valve body.

If it has the aluminum regulator valve just replace it with the steel valve.

wonder why it never did this in 203K miles that this valve body was in the original trans? It went almost another 1500 miles in this trans before showing up.... like I said it shifts fine, works fine, just sounds crappy
I plan on doing a fluid/filter swap soon just because this is a fresh overhaul.... in case I missed something in the fluid cooler flush I did while the trans was out..... sounds like a good time to address this.... thanks guys....

body on this 92 is still better than that on my 96, and better than many trucks 15 years newer.... so I will drive it til it crumbles even if I gotta swap engines and/or another trans..... I like not having payments, too much.