[ROVERNET - UK] riddle me this-sudden 3500s road noise

[peter king]

Hello all. 

In anticipation of a cold weekend under the car, I wonder if anyone has an
idea for what might cause a sudden occurrence of road noise and vibration on
my 3500s? I've determined only that it is not engine-related, as the
vibration does not stop when I shift into neutral and coast. The vibration
came on suddenly at about 60 mph, and now begins at about 45 mph, and is
quite pronounced if I go over 50. Tires all look fine, but that deserves
closer inspection. 

Thanks in advance for any recommendations you might have.

Peter King