Mystery rumble at speed

[MT Tatman]

So, after having my U-joints fixed and driveline put back in, I seem to have a new rumble. It is an Oscilating rumble, meaning it sort of comes and goes but in a pattern. Like the sound the Old school Cylon's from Battlestar Galactica!!
So folks, any thoughts? could the driveline be slightly out of balance? Maybe it is my Transmission? It is not a severe shake, just an annoying rumble that pulsates in and out. I don't feel comfortable taking it on the highway and I do need to go places....Bummed.....Rob.

 

[Bad_Vision]

could be rear differential hum?
i know mine sings in and out at 60+ really common for yota axles.
you can silent them down a little by using a higher viscosity gear oil like a GL6 80 140 gear oil