[Kintaro_Oe]

I had this same issue after installing my mazworx bellhousing with the driveshaft they provided. Ended up being the universal joint not being lubricated properly.

When I was holding the driveshaft (off the car), i grabbed the u-joint and would move it around and noticed a few dead spots where it wasn't smooth and sort of catching a bit. I had Drivelines NW replace the U-Joint and voila, vibration gone.