Vibration problem from the rear

So i recently started to get vibration from the back where i would be driving in the highway and all smooth and all of a sudden vibration comes in the rear and i can feel it being the rear and not the front. Its not a constant vibration and only happens at high speeds. I also had the problem where the car would make a clunking noise when shifting from rear to drive if that leads to it? Help would be very appriciated, my car is an 2001 bmw 330xi