I have this problem on Gigabyte motherboard.
And someone reports it exist on KDE Neon
Looks like a bug in Plasma or pulseaudio
lspci -nnk | grep -A2 Audio
00:1b.0 Audio device [0403]: Intel Corporation NM10/ICH7 Family High Definition Audio Controller [8086:27d8] (rev 01)
Subsystem: Gigabyte Technology Co., Ltd GA-D525TUD (Realtek ALC887) [1458:a002]
Kernel driver in use: snd_hda_intel
--
01:00.1 Audio device [0403]: NVIDIA Corporation High Definition Audio Controller [10de:0be3] (rev a1)
Subsystem: ASUSTeK Computer Inc. Device [1043:8354]
Kernel driver in use: snd_hda_intel