AU drivetrain vibration

[macman]

I had the transmission in my AU TE50 (5.0 auto) rebuilt as it had lost reverse, had a leak from the rear extension and wouldn't hold a gear when manually downshifting.

Got the car back and the transmission now feels great. That said, I still don't think it's holding gears when downshifting quite as it used to when I first bought the car but I'm not 100% sure as it's been a long time since I've been able to downshift!

BUT my main problem:

When at operating temperature, I can induce a quite noticeable droning vibration.

Only occurs between 80-100km/h and only when the torque convertor is locked in 4th and you apply light acceleration.

I took the car back to my transmission builder who told me that he didn't believe it was TC vibration or any issue with the transmission and that it was more likely an issue in the motor (pinging under load or something similar).

So, I've owned this car for over 6 years and have definitely had previous issues with pinging, mostly resolved now. But this feels nothing like what I've experienced and it certainly has never done this previous to the transmission being rebuilt. I've said all this to my transmission builder, he seemed to sympathise and didn't seem to be trying to get rid of me so to speak, but has told me he believes there's some other issue elsewhere.

Searching the forums I've read that using the wrong transmission fluid can cause this sort of thing, but there's no way he'd use the wrong fluid as he is a Falcon transmission specialist!

At this stage, I think I'm going to take the car to another transmission specialist for a second opinion but I'd like to know if anyone has any suggestions.