Driveline vibration out of now where! Help!

Well, this may not be as bad as i thought!.as i said, i changed the trans mount and with it set up on jack stands, it still did it. ok, i decided to take it out for a ride and the first thing i noticed is that unless im REALLY looking for it, i didnt notice it..After driving around for an hour, im starting to think it has always been like this, but i didnt really notice it until the trans mount let go and then it was REALLY noticeable! Now, with the new mount, i really cant hear it like i was and can feel it just a little but really have to be looking for it.. I still need to figure it out but im not as worried as i was because i do believe its back to normal.