Noticing a vibration and noise from the vehicle, an 03 Expy, when at interstate speeds. It is much more pronounced when in 4WD Auto than when in 2WD. I suspect it is a failing bearing or universal joint in the front driveline. Any good ways to test this that don't involve me laying in snow?

 

I can say with 99.99% probability that it is the u-joints in the front drive shaft. When in 2WD the front drive shaft does not turn, when in A4WD it does.