did the noise start after the tyre was fitted also which tyre did you have changed ,front or rears .one easy way to eliminate tyre noise is to replace the new one with the spare ,if it is a cure then thats the problem rear wheel bearings could be a problem if so jack up the rear and spin the wheel by hand you should not hear any noise with the good bearing ,but a faulty one will show its self as a slight rumble even when spun by hand ,can you feel any exess play in the wheel bearing .also i would have thourght that your mechanic would have checked each front bearing first ,by jacking up each side in turn and then putting the van in gear and running each of the the front wheels in turn , that would have shown up any exess noise in the bearings .by the way you van is fwd so no prop to worry about .if your wheels were out of balance you would feel a vibration through the steering wheel .but your main starting point will be if the noise and vibration started just after you changed somthing and work from there
