Inquiring about the sounds of silence

[Dlavjr]

As I get deeper into meditation, there are more things I pick up on. When I'm in pure silence, and I quiet my mind, I hear both this hollow void of emptiness, as well as a high frequency hum. I've gotten curious about them both, and I've tried to isolate and investigate them individually, but I can't quite put my finger on where they may be coming from. The high frequency hum seems to be a ringing in the ears, so I can only assume that's a physical phenomena, but the sound of void emptiness still escapes me as an unknown. Has anyone ever investigated the sounds of pure silence? What conclusions can be drawn about the "behind the scenes" of the ever busy mind? 

[Nahm]

@Dlavjr Very astute man.