I suspect I might need to replace at least one side rear wheel bearings. I've just noticed an intermittent hi frequency vibration and noise during road driving. Is there any way to check these without taking the whole axle assembly out to inspect? I've jacked both wheels off the ground and spun them but they don't feel or sound rough. Are they suppose to be re-greased as a service item? I've checked the Diff oil for metalic particals just in case but that seems clear.