help! front end "not so good vibrations"

[spotted dogs]

I have noticed that at highway speed (90+kmh) I am getting a high frequency vibration and accompanying loud drone/hum out of my front end. I had an balance/alignment done in Aug so I doubt it's that, steering fluid good....it almost feels like the 4 high has kicked in and is not kicking out (the in dash light does not come on)... I am wondering if it is the sensor that kicks in the 4 wheel drive is malfunctioning...or a wheel bearing? (but I cannot tell if the noise is limited to one side).
At lower speeds the noise is almost too subtle to hear but it is there. any hints? ( I' m at 109k km on the vehicle- 98 ltd sohc NOT awd)

 

[pagz]

how old are your tires? Are they wearing unevenly, maybe cupping, is the treads different colors? You may need to replace them.

 

[spotted dogs]

tires ok

the tires (bridgestone dueller at) are ok -lots of tread left there probably is 60% tread life left . I think can eliminate that as there really is nothing obvious tire wise to account for that and the sound really is too loud to be tires (I have never heard tires get that loud on the road).
thanks for the reply though.