A Sound in my Room

There is a sound in my room. I do not know where it comes from, cannot even adequately describe the sound. It seems to emanate from hidden place - perhaps even the walls themselves. It is a kind of hissing sound - like the static of an untuned radio. A crackly and rumoured static. It sounds like the sea also, a rushing kind of noise. Water over stones. No, more like a river than the sea. There is no rhythmic pulse of tides. What is it? I thought it was my dinner on fire at first (grilled fish and mushrooms) but these have now been eaten and the noise continues. Perhaps it is some kind of interference on the laptop, but it seems to be making the usual heaving groaning sounds, and the sound now seems to be coming out of the air... and now it's stopped.