The wheel bearings are quite strong and don't normally give out unless submerged in water etc. Think you may have a bad CV joint in your axle which while not under load is very hard to detect. Have you checked for a broken boot which may have let the grease escape? If you think a joint is dry, try cutting the band on the shaft side (small) and slide a spray can extension of some white lube under the bellows and shoot some white grease in. Then seal the bellows with a tierap. If the noise goes away you have found the culprit joint. The outers are not rebuildable but the inners are. If you try a used axle, cut both joint collars off and slide the boot down to make sure there is a proper amount of grease in it, then reband it and install.

Good luck,
Tobias MB
4 MBs

PS As always, please tell the forum what you find to resolve your problem. Thanks