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...

 

Okay.... Sorry a lot things came up and I couldn't log in to update.

****SOLUTION*****
It wasn't engine problem.
It wasn't transmission or misfires or gasket issue.
It was just a bad CV axle on the driver side.
My dad remembered that my brother some time ago had similar thing happen to his Scion TC. The CV axle balls would lock up at certain speed.

I replaced the CV axle and viola!
No more strange knocking, no vibrations, I took the car up to 65mph and no issues!

Thank you all for the scare and horrifying me with your "will need new engine" or my "transmission is gone" But glad I talked to my dad. Thanks to all who commented.

Hope this will help someone down the road...

Cheers....