[janusz]

Looks like bearing as it holds magnetic sensor for abs and stability control.
Best to replace it asap. Do not got for cheapest bearing but also do not buy volvo branded. Search here on forums for wheel bearings. Some time ago I have run own investgation to find out who makes bearings for volvo: skf and fag. Dont remember now who makes fron or rear but oem bearings can be found for 70-80£ while volvo branded cost circa 200£.