"I bought my phone in US and everything is fine, except the creaky sound when I press the side buttons like volume and record. This weird sound comes from the plastic. Can someone confirm that it is OK?"
There've been extensive discussions in HoFo about creaks on the left side of the front (in the 1, 4, 7, and Calendar keys, for example), but I haven't seen any reports of creaks in the right side keys like you describe. My E51 does not creak on the right side (volume buttons), but it creaks along the left side of the front -- it's annoying, but I haven't seen any degradation in usage.
I tried out two E51 display phones in the NYC Nokia store, and they creaked, too, so I have kept my original E51.