Step on stair makes clunking sound

[fsa297]

One particular step makes a loud clunking sound when stepped on. It's not a quiet squeak, but almost as if there is a significant gap between the tread and whatever it is resting on. The stairs are carpeted, but looks like an individual piece of carpet for each step instead of one long piece of carpet covering the whole thing.

Is the fix to nail in the tread more securely? Is that relatively easy to do, or would I need to call someone in?

Thanks in advance.

 

[Tigercubrider]

Can you get under the stairs to see?

I would screw it. But you need to have something to screw into

 

[foxhole]

May have hard board under which is flapping on worn step.

 

[fsa297]

Unfortunately the bottom and sides of the stairs is paneled off, so I can't see under it.

Hard board, meaning the tread board?