Blackberry Keyboard problem?

Hi i have BB 9900.

I love the sound of "clicking" when typing the keyboard.

However, one of my keys does not make that clicking sound anymore.

It still works, but I don't feel it clicking. Could you tell me what is causing this problem

and any suggestions on how to fix it?

Thanks for your help :)

Could be just a hardware problem. How long have you had it?

just bought 2nd hand one.
should i dismentle it to see whats going on underneath the keyboard?