"It's quiet out here; too quiet. I've always wanted to say that."
--Templeton "Faceman" Peck of The A-Team; The Taxicab Wars, aired 11/01/83.

One of the most overused movie tropes of all time. It is a very easy and well-recognized way for the scriptwriter to indicate that something exciting is about to happen. It has reached the point where few, if any, movies will use it seriously. It still appears in any number of comedic movies, although it is ridiculously hackneyed even in the context of ├╝ber-corny jokes.

Donatello: The perimeter's quiet.
Leonardo: Yeah, a little too quiet.
{they knock out the only two guards}
Donatello: Well, that was easy!
Leonardo: Yeah, a little too easy.
{they see Raph tied up}
Donatello: Look! It's Raph!
Michaelangelo: Yeah, a little too Raph!
Teenage Mutant Ninja Turtles II, 1991

The origin of this phrase is uncertain, to say the least, but general consensus is that it almost surely comes from an old western. The most likely candidate is a 1934 film starring John Wayne, The Lucky Texan (Which can be found here). If this is not the origin, it is at least the film that first set it up as a cool thing for the hero to say in the minds of America's youth and film-writers.

For the sake of completeness, I will also mention the earliest quote that contains the phrase, although it is in a different context. In 1920 Marcel Duchamp was quoted as saying "One doesn't drink here any more and it's quiet, too quiet." However, he was just commenting on the effects that Prohibition was having on the city, and this had nothing to do with premonitions of impending doom.