I have heard this noise for quite a while now and at first I attributed it to my aggressive tires just making road noise and it always did it, but now I'm really not sure after so long I forget. It's maybe very slightly vibrating, but it's mostly smooth and as I drive I get this pulsing sound starting from low speed and gets faster until it's just a droning noise at highway speeds. I think if it was just the tires it would be constant, not a pulsing. And if it was my rear end or something why would it pulse either?
My best guess is my tire is ever so slightly off balance, or someone told me there's a bulge somewhere on it throwing it off slightly but not enough to vibrate it. Does this make sense? Thanks.