I'd guess that your front bevel gear is NG, best checked by an experienced Volvo dealer tech. The part alone is about $2,500, not including labor (3-4 hours flat rate). Have them check all tires for being the same runout as if you (or someone before you) only replaced one or two tires leaving worn tires on the other wheels rather than replacing all four at the same time as Volvo highly recommends, bevel gear damage results. If you have a mismatch of tires now and your bevel gear is NG, you'll also need 4 new tires or you'll ruin the new part as well.