change wheel bearing of ONLY those wheels which are creating noise. there are very thin chances that all 4 go bad at a time.
buy new Koyo bearings from market. i bought for my Liana for around 1700 per piece original Japanese Koyo. chinese were available too for around 700 per piece. another thing - which is MOST important - bearings contain small roller balls inside - these mechanics hammer them very very roughly with full force to make them sit inside the wheel hub - NEVER do it. this will dis-locate the small balls inside and the bearing will be useless very soon. so, make sure the bearing is 'pressed' inside with a press machine - he takes 50 rupees per press and the bearing fits in like knife in butter with 100% accuracy..