Sometimes I have dreams where things are inaudible. However, I can still know what people are saying, and can perceive the affects of sound as if they exist, but I don't actually hear them. It's very strange, but like Delphinus suggested, it can be used as a dream sign. Perhaps use earplugs, because they seem to convey more of the "lack of sound, but you know it's still there" sensation rather than just pure silence.

Anyway, hope that helps. Good luck to you, Fisherdec, and happy lucids!