How fast is the vibration? The driveshaft rotates at something like 3x the tire rpm, so if it's a medium speed "brrrrrr" it is probably more wheel related. If it is a high speed thrumming, it is probably the driveshaft. My driveshaft support bushing problem made a "thrumm... thrumm.. thrumm.." vibration, and it would also appear while accelerating through certain rpm ranges.