Have a microphone? Try recording it. To list out all the plausible explanations, it is either a creaking in the house, a popping in your ears, or an auditory hallucination. If it shows up in the recording, it is a creaking in the house. If it does not, it is one of the second two. Then, to extend the analysis, record an hour before meditating, the hour of meditating, and an hour after meditating. Then later play back this sound, or look for spikes in a visual representation of the sound file, and see if the noise rate/intensity really does change during the time you are meditating.
If you do this, let us know the results.