My wifes BB had the same problem 6 mo's in and I had it replaced under warranty. If yours is that new I would demand a new unit in hope of saving yourself any issues down the road.
i have a 6710 with the same issues.. i pretty much just write it off to the fact that they are hard plastic keys and usually some pressure through flexibility added to it would simply make it sound different given different temperatures. go figure...
One of the usual reason for this problem showing up after a while is that something sticky has got spilled on the keyboard, it might be worth opening it up and wiping the inside of the case and the keyboard itself.
Mine doesn't "creak" per se, it clicks with each key press. So I'm not sure, I tried compressed air, didn't work. Not sure if clicking is normal either. I don't recall co-workers bb's doing that