Is it normal for my MacBook Pro (unibody) to creak in some spots?
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.