to rush out of a den, rustling, whispering
窣 centers on sudden, swift emergence from a confined space, like an animal rushing out of a den. The rustling and whispering senses extend this idea to quick, soft sounds that break silence abruptly.
窣 combines 穴 (hole, den) with 卒, which likely contributes the sound and possibly the idea of sudden movement. The exact historical development is uncertain, but the character is used for swift emergence from a confined space.
A creature bursts out of a cave (穴) and the sudden movement (卒) makes a rustling sound. The swift exit and the soft noise are both captured in 窣.
For ソツ, imagine a small animal rushing out of its den so quickly that it makes a 'sots' sound: sots -> ソツ, like a sudden rustle.