Best way to make ambient sounds play?

I want to have tiles in the tilemap play ambient sounds, such as running water, and I was wondering what the best way was to do this because having a sound play on every tile gets really CPU intensive fast, plus it messes up the audio and other unpleasantries.

Rather than attaching a sound to each tile, it's probably better to attach it to an invisible sprite and then place the sprite in an area that needs the ambient sound (tweak the settings so that the distance/volume is correct etc). I usually just create a bunch of these invisible sprites, 1 for a waterfall, one for birdsong etc and then place them strategically on my layout.