h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

It is generally not a good idea to go around shouting your head off in the great outdoors. In some places, even just talking at a normal level can disturb the local wildlife- so it is best not to talk if you don't need to.

And I'm sure we've all seen in cartoons where the character sets off an avalanche with a loud yell, burying themself in snow!

Deus Ex Machina

But talking is good around some animals (bears for example) then they hear you coming (and can run away) and it you don't appear to them suddenly. If you happen upon a female bear with cubs suddenly it can be deadly. So its often advised to make a bit of noise so they can hear you from a distance off and avoid you . ..

I suppose it depends on what kind of country you're going through, really.

On the other hand, don't expect the countryside to be quiet!
Apart from the indigenous wildlife there may be farm machinery operating nearby.
Don't expect sweet smells either - especially if a farmer has been muck spreading.
Also, do watch your step, grass can conceal all sorts of nasties from dung to thistles or biting insects.