Sound of a spring

BOING

Think of the noise a cartoon character might make when bouncing on a trampoline or after a sudden, elastic rebound.

Sound of a spring" plays on the double meaning of "spring"—both the coiled metal object and the season. When a spring (the metal kind) bounces back, it makes a classic "boing" noise, like in cartoons when something snaps or rebounds. The word itself is onomatopoeic, mimicking the sound, which makes it a fun, direct answer for the clue.