My RAV4 sometimes has a vibration. This happened maybe 2 weeks ago as I was driving down the road. The vibration seemed really bad but I stopped the car and then started driving again and it went away. It was fine after that but today there was a significant and very noticeable vibration. It was noticeable around 35 or 40 MPH. After a short while, this vibration also went away
I did notice something else. If you open the window in the back seat (either side), you can hear a kind of oscillating vibration that effects your ear in a weird way. This particular sound seems much more consistent or possibly it is happening all the time. If you open windows in the front seat, you don't hear it. I seem to be able to hear that even though the other more serious vibration has been more intermittent. The more serious and intermittent vibration does not need the window open to be noticed and is not just a sound but a vibration.
I will probably have to call the mechanic this week is my guess, probably I will call him on Monday