[chris (OP)]

Amanda Tweeted to ask:

"Why do we snore when we’re asleep but not awake?"

What do you think?

[Colin2B]

I think it's due to lack of muscle control. When we are asleep the muscles of the throat relax and narrow so the air can more easily start the soft flap at the back of the throat vibrating.

[evan_au]

(Oops - overlap with Colin2B; this seems to happen more often, now I am in the same timezone...)
For some sufferers, muscles in the throat or tongue relax during sleep, obstructing the airway.
See: https://en.wikipedia.org/wiki/Snoring#Causes

[RD]

.... When we are asleep the muscles of the throat relax ...

Some only snore when they are relaxed as a newt, (or under anesthesia). 

[SquarishTriangle]

Some people seem to snore when they are awake. I have sat next to them on the train...