My little dog has just gone outside. She lets me know that she wants out, by staring at me and transferring thoughts until I get up and open the door for her. When she's ready to come back in, she barks. Just the once. A sharp, loud "Woof". It may be repeated a couple of times if I don't let her back in within a minute or so, but it's not a constant 'barketybarketybark' as a lot of dogs are want to do. I love hearing that bark. It means that she's back safely, and all's well with the world. Another doggy noise that always reassures me, is the glingling of her collar tags when she's decided to play 'hide and seek' with me, and I haven't been able to spot her lurking in the undergrowth, or behind trees. When I hear that, I know she's safe. Playing silly wotsits and so, but safe.
There was a bad train crash in Southall a few years ago. I was with my ex who lived very close to the station. Normally, Southall is a very noisy place; cars jammed bumper to bumper, horns blaring, stereos blasting, people shouting, but that night of the train crash, no traffic was allowed with half a mile of the station, except for the rescue teams. All was silent save for the emergency vehicles and the helicopters overhead.
When the bombs went off last summer, the trains in my back garden stopped. The silence was deafening. Conspicuous by it's absence if you like. I hated that silence.
On both those occasions, I was relieved to hear the traffic and the trains running again. It meant that although something terrible had happened, life was starting to return to a semblance of order once more.
I've been waiting for that solitary bark for half an hour now. I've been fretting and imagining that I'll never hear it again, but then I'm one of those people that worry. A lot.
There it is. I'm happy again. If you'll excuse me, I have to go and cuddle a small dog now.

Are there any sounds, or things that make you feel relieved or happy?