HELP:: Very strange knocking 40mph

Very strange knocking/vibration when getting up to 35 + 40mph.

Just got this car from auction.
Test driving and car has some unknown-to-me issue when getting up to 40mph and I dared not to take it any higher.

Sounds like something is knocking, vibrating, shaking the axle or underneath the car.
Going on straight road, very smooth pavement & no bumps.

I put the car on the lift and had a friend give a bit of gas to recreate it and seems like transmission trying to "break" when giving acceleration and jerks the engine badly..... Maybe that's what I'm feeling when I'm driving and it just "sounds" like something is "knocking"...??

See my videos from YouTube here:

Vid#1:

Vid#2:

These may help explain.

 

138k miles

 

It's definitely not balancing.
I know unbalanced tires + alignment issues.

This is more of hard "knock" or hard vibration or jolt that you feel very loudly inside the cab then you're driving. I at first thought an axle was loose or broken - making that knocking some every rotation while driving

 

If I understood you correctly... You're saying the issue is inside the transmission, correct?

My suspicion is that at auctions they use massive forklift tractors to move these cars around.... Can they mess up the transmission/transaxle internally if the car is "off" and transmission is on "Park" but they roll the wheels or drag them on the ground when lifting the car and thus making the wheels "roll" when the car is in "Park"..???

Not sure if that made any sense...