First thing that pops into my mind is ..
does the sound change with application of brakes..
or application of just the parking brake..
and..
does it change when you swerve left and right.
"Usually' noisy wheel bearings change when swerving ..
   the bad bearing/s being toward the quiet side..
or away from the noisy direction..
swerve left and it gets worse..it's often a left side bearing, if it's a
bearing issue.

you've jacked up and wiggled wheels ? ..
that's a logical first step ..
even an imprtant safety inspection in a case like this.

On 10/21/2013 6:59 PM, JRodgers wrote:
> Many, many times we Volk's have reported strange noises and asked what
> they meant - hoping to head off disasters. Well, it's my turn, it would
> seem.
>
> Imagine if you will, you are on a bicycle, and you have attached a
> rectangular piece of card board to the front wheel fork so that the edge
> of the card board sticks out just far enough in to the plane of the
> rotating wheel that the card board strikes every spoke as it passes by.
> At slow speed its an innocuous  put-put-put-put, but as the wheel speeds
> up the tempo changes to a distinct whir like a small motor. We all did
> this as kids. Right? Well, I've got the whir without the cardboard - in
> my Vanagon.
>
> This whir sounds just like that cardboard but it begins to become
> noticeable around 50 mph - gets louder with more speed and disappears in
> road noise around 65 mph.
>
> I am concerned! There is no vibration associated with it. I am wondering
> if some bearing issue is developing - or other.
>
> Anyone care to speculate?
>
> Thanks,
>
> John
>