adverb, adverb taking the 'to' particle
rustlingly; with a light rustling sound
Describes a soft, dry rustling sound, like leaves, paper, or fabric rubbing together. Often used with と.
The fallen leaves rustled in the wind.
She rustled the paper bag as she took out the snacks.
Onomatopoeic formation from the light, dry rustling sound it represents. The exact origin is uncertain.