Silent noise while running simple OSS program and moving mouse?

From: Evgeniy Khramtsov via freebsd-multimedia <>
Date: Sun, 16 May 2021 22:01:31 UTC

I wrote this simple OSS program that outputs sound from microphone back
to the speakers (the close() and stuff is omitted):

It works, though for some reason I get some silent noise while moving
mouse around. Any ideas what could be wrong? Thanks.