I attended a lecture given by Zahi Hawass some years ago and he said then that he thought that there was a chamber yet to be discovered.

He didn't elaborate and when he invited questions I'm afraid my attempts to get noticed at the back didn't succeed so I know no more about his thoughts on this.

Actually he was bit irritated because after delivering a lecture about the pyramids all everyone wanted to know about were recent claims about Nefertiti's mummy having been identified by Joanne Fletcher.