iPhone 4s / hiccup speaker

My iPhone 4S has a problem in speaker which is weird.

When I'm in calling has moments where I stop listening, I move me to another place and hear back, a few moments later I no longer hear again or hear with interference but without understand what the other person says. Sometimes give a little click in phone and hear again. Sounds like when the other person has losing a signal and we listening to that sob and we only hear the words by the half.

I've changed the speaker for a new one, but not fix the problem. I've read that some people have the problem of not hearing anything, but in my case is intermittent, the cause will be the same?

Any help would be appreciated