Volvo bearings used ?
How any miles done since ?
If they're Chinese aftermarket parts.... I wouldn't discount them.
Could also be a prop shaft bearing worn or donut wear.... rear CV Joint or rear driveshaft on its way out. Could also be worn rear brake discs that are out of balance.
Is the rear wheel/caliper hot after use ? Maybe the rear caliper(s) are sticking, this would cause a rumble and vibration and isn't uncommon on an XC90. It needs good scrutiny on it, by a good trusted mechanic, rather than guess work.
Hope you get it sorted.
Report back what you find so it may help others
