Driveshaft or rear diff noise

[frankvan]

2005 AWD Sienna

I get a whining noise coming from under the center of the van that varies with vehicle speed (not engine speed or engine load - does it accel, coast and decel). It starts at about 10 mph and gets higher pitched until it disappears at around 30 mph. Has anyone experienced any problem with driveshaft supports or the rear diff? I haven't had a chance to get it onto a lift yet as its -20 and snowing right now but am curious what i should look for.

Thanks

Frank