The most common source of grinding is worn out brake pads grinding on the rotors. Jack up the front wheels and remove the tires to get a good look at the rotors and pads. If you must replace them, do both sides.
Wheel bearings generally have a long wearing out-to-worn out cycle, and typically make more of a roaring sound that is more pronounced when going around corners. The diagnosis for bad wheel bearings is play in the front wheel in both left-right and top-bottom wiggling. Jack the car up for this, but leave the lug nuts tight. Try to wiggle the tire toe-in and toe-out. Then try to wiggle the tire camber-in and camber-out. The play can be very subtle but should be the same for both wiggles.
I hope this helps. Pat yourself on the back already for not driving the car further and doing more damage. I recently bought an XC70 where the PO wore the rotors through the face and into the fins! He had to replace pads, rotors, AND calipers!
Grinding noise
; '00 XC70, '99 S70 AWD, '99 XC70, '98 XC70, '98 V70 (2), '98 S70; 850 wagons (2) - 10 volvos 
