Bummer about the whine. I agree with Steve McMahan, find the cause of the whine first. Easier said than done unless you have a diagnostic kit like chassis Ears, where you can clip one or more Piezo Chip clamps onto different parts of the AODX (assuming the whine is definitely from the AOD). Then you can select up to 4 or 6 (depending on the unit you get) separate vibration (sound) channels to help locate where the whine is from. If it is from deeply internal in the AOD things may get confusing in the event the vibration is traveling from one end to the other. If he sound is not coming from the AOD you can keep clamping the sensors around until you narrow it down.
The chassis Ears solution has the basic system using wires from the Piezo Chip sensor clamps to a breakout box. It works well, but running and managing all those cables (thin wire) can become a real PITA. They hace a BlueTooth enabled sysztem also, which I have seen lots of folks gripe about - so I did not get it. Finally, they have a system with 4 wireless transmitters that connect to very short Piezo chip clamps, then send the vibration signals to a radio receiver. That is costly, but so much easier to use. It comes with only 4 radio transmitters, but you can purchase a 5 and even a 6th unit if you like.
https://steelmantools.com/collections/noise-vibration
I see Wake Forest, NC, is just over 600 miles from our place in Pittsford, NY (suburb of Rochester). It is a bit far for either of us to travel for this diagnostic effort. Otherwise I would be offering to have you use our Chassis ears equipment, as well as a home brewed solution to capture vibration waves. However, we do travel down to Florida a few times a year, We drive the I-95 to and from FL, which puts us really close by your community. We just got back from our Winter visit, and may not be going back down until Summer. My guess is you don't have that kind of time to wait with this situation. If you are interested in having us swing by on our next trip to FL, or think you would be able to bring the Mustang up to the Rochester, NY, area, let me know and I can begin to make plans.
If you determine the whine is from the AOD, and you feel it better to replace it with a 4R70W, I would be the last to try to dissuade you. I swapped in an AOD in our 73 Maach 1, and I am very happy with the results. But, had I known then what I know now I would have done a 4R70W initially, just to get away from the need to adjust the Throttle Pressure Valve setting, using a a dagnostic oil pressure and special spacer at the carburetor linkage. It is not hard to do, it is jus tedious. With a 4R70W, and a nice controller box, not only can we adjust the Throttle Pressure Valve setting, but the upshifts (and downshifts) can be programmed as opposed to doing like I didm increasing the Throttle Valve PSI up to 39 PSI to increase the road speed before the 1-2 and 2-3 upshifts occur. I finally got it dialed in, after a few TV adjustment sessions, but it would have been nice to do all that from a controller unit.
I find myself standing on two footpads with our AOD. On the one side I hope the AOD has a long life and proves to be very reliable. On the other foot, I would love to have any excuse to swap in a 4R70W tranny and controller, but I prefer to not spend the money to do it unless it is really needed. Frankly, the AOD is doing a great job. But, I get paranoid about "something" happening that causes the TV pressure to go below 30 PSI, and the tranny getting toasted as a result. Lots of AOD equipped vehicles had that happen when a plastic bushing on the original engine/tranny build was used, and later that plastic bushing got brittle and failed. The TV cable would go limp when the bushing was no longer present, and the AOD ended up getting toasted. So, I am preparing to install a flat LED display inside the Mach 1's center vertical bezel,, and run a wire down to a pressure sending unit that will be connected to the TV test port on the passenger side of the AOD. That way I can have a constant readout of the TV pressure under all driving conditions. Were the pressure to drop below 39 PSI I know I would feel it in the shifting behavior of the tranny, but would prefer an immediate look at the PSI value without having to connect the Oil Pressure Gauge and deal with the cable spacer block. Lazy? Me? Maybe. But I am going to do it anyway.
An aside, using the center vertical bezel as a mounting location for the TV PSI LED is a kind of natural place for me to mount the display. We do not have the 3 analog auges that were an option, as our original instrument panel was all idiot light equipped. I installed a Dakota VHS analog gauge cluster when we first got the Mach 1. I also mounted a Garmin Drive 51 GPS and (backup) camera display unit in that same area, just beneath the air conditioning outlet. All that was in that area of the bezel is a plastic "MUSTANG" filler/delete plate. If you want to see visually where I am speaking of, or are interested in how the Garmin unit mounting looks you can check out the following YouTube video:
https://www.youtube.com/watch?v=xSxEBNDKp7o
