Is it normal for my MacBook Pro (unibody) to creak in some spots? I bought a new MacBook Pro 15-inch model with highest specifications in this June. I also installed Lion and have updated it.

Moreover, I would like to ask somebody who already has the same model, or any MacBook Pro, if it is normal to hear ticking sound when you push some spots on the bottom of the computer (beneath where the trackpad is).
That's not "ticking," that's a creak from the flex in the aluminum chassis. The MBP is not a brick of aluminum but a computer inside a hollow shell. While built solid, there is still play in the materials. 

The sound you're hearing is likely the case pressing against the RAM, the battery connector, or the metal protector right beside the battery connector (or perhaps another component inside the machine).

If you are worried, take it into Apple. But they'll tell you the same thing.