Check them closely for wear. Look for pitting on the rollers and races. Also, if the grease is discolored, as in black, may indicate damage.
I recently had a shop pack my bearings before a trip to WA state, only to find he didn't check for wear. Right inner bearing was smoked, happy it didn't seize during the trip. Just kind of low vibration into the frame.
Figured it out when I was on a right hand freeway curve, the noise stopped...