Focus rear wheel bearings?

Hi everyone, I got a 2008 Ford Focus, an the situation is that I hav been heaving problems with the rear wheel bearing (noise). I repleced it for 2 times on last year, first the bearings presented factory defects (was generic brand) so the mechanic said a brand change was better, it were on last august, but nowaday I heard a little noise.

What can I do to fix it?

These bearings has no lubrication by myself.

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