Can hear mic feedback with Plantronics C520

This USB headset, new to me:

Bus 001 Device 005: ID 047f:c035 Plantronics, Inc. Plantronics C520

has an issue with seemingly automatic loopback, where - if I do not enable mute on its cord - I can hear the mic in my earphones. How do I disable this? I have checked, and PulseAudio does not have a loopback module enabled so far as I can tell.

welcome to Manjaro

Pulseaudio does not normally have a loopback module enabled because the audio is likely to be delayed within Pulseaudio.

If you can hear microphone audio without any delay, it is probably due to a microphone monitor control or loopback control in ALSA

please post full response to

 arecord -l

to show audio capture devices available in ALSA