Check the mounts on the engine and transmission.

If the shaft going into the back of the transmission isn't parallel to the shaft going into the differential, the driveshaft will be subjected to a variation in torque every revolution. That could have led to the failure of the original shaft, and it could lead to the failure of the replacement.

The shafts won't be parallel if one or more of the mounts is bad, and the engine/transmission is out of position. That would explain the knocking noise, too.

Has the car ever been in a collision or been subjected to a hit on the underside from a speed bump, etc?

 

It has been in an accident, but just on the drivers side.

I took it to NIssan and told then to drive the car. They drove it 4.5mi and couldn't find anything.