HELP!!

I have a very serious question, i have a mazda demio 121 and i have a bad problem. I replaced my bearing twice and it sounds like the same problem, alot of noise, sometimes loud knocking sounds and at times the car seems to go down a gear as if it were a manual?? it an automatic..... all the mechanics so far tells me its the bearing again even though after 1 week of changing them the sounds and steering vibrations came back... :S

Its a grease issue on one of the wheel bearings, My <a href=http://www.pugimazda.com/search.cfm?t=N&lid=2> Mazda 6 </a> had the same problem. got it fixed, came right back a month later. it really doesnt hurt anything. get it checked.