Eurovan front end noise

I have a 2002 VW Eurovan Weekender w/90,000. A couple of thousand miles back once or twice I noticed a lack of engagement when accelerating suddenly at 35mph. A few hundred miles ago I began to hear a very faint, almost undetectable whining sound that my mechanic insisted was nothing. With a few hundred more miles it became a very noticable whining sound coming from the front. Beginning at the top of a little hill with the engine off and the van in neutral I began a slow roll, the almost crunchy sound begins as soon as the van starts rolling and stops immediately when I apply the breaks. Also, you can hear it at all other cruising speeds. My mechanic put it up in the air and confirmed you can hear the whining/grinding from ten feet away. I am aware of the history of the Eurovan's transmission and have made some calls to experts that say the transmission/transaxle would not make enough noise to hear it in the cabin while driving, that it's got to be wheel bearing/axle/brake related. ?