You are entering classic sleep paralysis with hypnogogic sounds. If you can get to that place reliably, you can take the next step into a full lucid!

Try reading through the tutorial section, particularly thehe WILD techniques. Those should answer many of your questions. Others will surely come along here with more experience.

When I get to the point you describe, it is very exciting for me because I know it is just one tiny step into a full lucid dream!