Zoom does a lot of audio filtering to screen our background noises and emphasize human speech.

That helps people when they are talking, but usually causes bells to sound terrible.

However, there are ways to eliminate the filtering, either all the time, or just when one is inviting the bell.

This Zoom Help page will walk you through the steps: https://support.zoom.us/hc/en-us/articles/115003279466-Preserve-original-sound.