Grinding noise....97 Aerostar

I can hear a rubbing or grinding noise coming from the front half of the car. My mechanic can't recognize which noise I'm talking about - probably because of all the other noises. Sounds to me like it's in the front half of the car. Wheel bearings all checked and OK. Full lube done regularly and nothing out of ordinary noticed last time.
Hear it only when rolling - slow or fast Any idea from the genius or shade tree folks? U-joint, trans, rear end?

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