The "sound of crickets" in background

[gary00k]

Hello, I've tried to use this DSP FX with my STM32. It works, but I noticed there is something like the quiet sound of crickets in the background. It lasts about 13-15 seconds after stopping input sound. This sound is the lower, the more different Shift value is from 1,0. My sampling frequency is 48kHz. Could you tell me what to do with it? I didn't notice this bug on your video.