Rldzhao, did you replace all of your bearing or just the one that was bad? I don't have any of the usual symptoms of bad bearings so I'm thinking this is just a fact of life with the stoptechs and will add knockback springs. I'm not big on hitting rumble strips but our tracks our here do have lots of elevation changes and compression turns that really load up the suspension and bearings and cause noticeable knockback.
I also spoke with bimmerworld and their vote goes to knockback springs. They said they've seen few if any wheel bearing issues on the e90.
I certainly will keep an eye on my bearings though.