You should open a ticket and record that extension’s calls. I’ve been having issues with two deployments of S500s with “variable” talkers. People who start soft and start talking loudly or move the phone handset to a different position. Calls can go to “fine” to clippy and loud in a heartbeat. Seems to happen to women more than men, but I have instances of both female and male voices triggering this.
Please be the 3rd of “100k phones sold” to report this important problem with S500s.
Private message me and I can provide you with recorded samples for reference.