Place it as a break between two scenes, after the dialogue has finished and before the next scene begins. Keep it on its own in that spot, then return to the main audio, so the break reads as a deliberate change rather than an extra layer.
O tym dźwięku
Tralala 1 is a short clip of about ten seconds built around the sung syllables tra la la, repeated as a simple refrain. It has a light, easy feel that suits a brief, playful pause rather than a serious moment, and it keeps its focus on that single phrase from start to finish.