。
I heard the rustling of leaves.
Literal
Tree-[possessive-の]-leaves [possessive-の] rustle-rustle [called-という] sound [subject-が] was-heard.
サラサラ is a light, dry rustling mimetic — paper, leaves, sand, hair. The frame X という音 ('a sound called X') is the standard way to name a specific sound in Japanese, with という labelling the mimetic as the name of the sound. 聞こえる ('is audible / can be heard') is the passive/potential counterpart of 聞く, in the same family as 見える vs 見る.