The wriggling is relatively faint. Less than half a millimeter of wriggle. To do so, put the BlackBerry on a flat surface, put your finger on the D key (the one with the tiny bump), and then lightly rub around this key. The keyboard may wriggle a tiny bit. This is normal.
I don't notice this during normal use, and this type of barely perceptible microwriggle has existed on all BlackBerries dating way back to the 950's.
Your unit might have worse than normal wriggle, and if it truly interferes with typing ability, then borrow another same-model BlackBerry to test. If it works much better, then yes, there's a defect. But a tiny bit of wriggle is normal.