What I hear while lying in bed in the dark at 6:10 a.m.

The first sound I hear comes from the fan. It is mostly a low, monotonous drone. But then there are subtle groans in brief moments when the fan seems to be exerting more effort. These moments come every three or four seconds and last about a half-second.
Mmmmmmmm-yu. Mmmmmmmm-yu. Mmmmmmmm—this is the continuous drone. Yu—this is the extra-exertional groan. The groan sounds like a car’s engine—softer, far away; then louder, coming closer. Except the car is not driving on a road perpendicular to my ear. Instead, the road is in a circle that loops out away from my ear and then back around. It is when the car comes back around that I hear the groan. 
Other than the fan, there is the sound of silence. It is like the static, salt-and-pepper channel on a television, turned down to the lowest volume. Or, like a million bugs in the trees at night. Not big and loud cicadas; more like little mites, whispering softly. And so many of them. Ssssssss. But the ‘s’ sounds too much like a snake. Silence doesn’t stick out its tongue or slither, so the ‘s’ can’t be right.
The sound is consistent. There is no inbreath, no reprieve like the groan of the fan. Just one soft, constant, slightly high-pitched exhale. So I assume the onomatopoeia for silence should have only one letter.
—If it’s like the bugs, though, it’s not completely constant. If it was recorded and slowed down, the sound line might have slight wiggles.
I try out other letters. Tttttttt. Yes, maybe ‘t’ is closer. Actually, more like this: teeeeeeeeeeee. But there can only be one letter. So maybe just ‘e’ then. Eeeeeeeeeeeee. That, as of now, is my best guess at the sound of silence.