Try this first:

killall pulseaudio; pulseaudio -k  ; rm -r ~/.config/pulse/* ; rm -r ~/.pulse*

Wait ten seconds, then run this:

pulseaudio --start

Should the approach above fail to correct the problem (it is only known to work on some variations), you can try this next:

killall pulseaudio; pulseaudio -k; rm -r ~/.config/pulse/* ; rm -r ~/.pulse*

wait 10 seconds, then reboot (putting the machine to sleep is not enough – fully power it off and then back on).

dmesg | grep "snd\|sound" -i

returns:

[    7.673796] snd_hda_intel 0000:09:00.1: Disabling MSI
[    7.673802] snd_hda_intel 0000:09:00.1: Handle vga_switcheroo audio client
[    7.673864] snd_hda_intel 0000:0b:00.4: enabling device (0000 -> 0002)
[    7.689821] snd_hda_codec_realtek hdaudioC2D0: autoconfig for ALC1220: line_outs=3 (0x1b/0x15/0x16/0x0/0x0) type:line
[    7.689823] snd_hda_codec_realtek hdaudioC2D0:    speaker_outs=0 (0x0/0x0/0x0/0x0/0x0)
[    7.689824] snd_hda_codec_realtek hdaudioC2D0:    hp_outs=1 (0x14/0x0/0x0/0x0/0x0)
[    7.689825] snd_hda_codec_realtek hdaudioC2D0:    mono: mono_out=0x0
[    7.689825] snd_hda_codec_realtek hdaudioC2D0:    dig-out=0x1e/0x0
[    7.689826] snd_hda_codec_realtek hdaudioC2D0:    inputs:
[    7.689827] snd_hda_codec_realtek hdaudioC2D0:      Front Mic=0x19
[    7.689828] snd_hda_codec_realtek hdaudioC2D0:      Rear Mic=0x18
[    7.689829] snd_hda_codec_realtek hdaudioC2D0:      Line=0x1a
[    7.701710] input: HD-Audio Generic Front Mic as /devices/pci0000:00/0000:00:08.1/0000:0b:00.4/sound/card2/input11
[    7.701824] input: HD-Audio Generic Rear Mic as /devices/pci0000:00/0000:00:08.1/0000:0b:00.4/sound/card2/input12
[    7.701942] input: HD-Audio Generic Line as /devices/pci0000:00/0000:00:08.1/0000:0b:00.4/sound/card2/input13
[    7.702061] input: HD-Audio Generic Line Out Front as /devices/pci0000:00/0000:00:08.1/0000:0b:00.4/sound/card2/input14
[    7.702188] input: HD-Audio Generic Line Out Surround as /devices/pci0000:00/0000:00:08.1/0000:0b:00.4/sound/card2/input15
[    7.702317] input: HD-Audio Generic Line Out CLFE as /devices/pci0000:00/0000:00:08.1/0000:0b:00.4/sound/card2/input16
[    7.702514] input: HD-Audio Generic Front Headphone as /devices/pci0000:00/0000:00:08.1/0000:0b:00.4/sound/card2/input17
[    7.948602] usbcore: registered new interface driver snd-usb-audio
[    9.392299] input: HDA NVidia HDMI/DP,pcm=3 as /devices/pci0000:00/0000:00:03.1/0000:09:00.1/sound/card0/input18
[    9.392341] input: HDA NVidia HDMI/DP,pcm=7 as /devices/pci0000:00/0000:00:03.1/0000:09:00.1/sound/card0/input19
[    9.392431] input: HDA NVidia HDMI/DP,pcm=8 as /devices/pci0000:00/0000:00:03.1/0000:09:00.1/sound/card0/input20
[    9.392471] input: HDA NVidia HDMI/DP,pcm=9 as /devices/pci0000:00/0000:00:03.1/0000:09:00.1/sound/card0/input21
[    9.392507] input: HDA NVidia HDMI/DP,pcm=10 as /devices/pci0000:00/0000:00:03.1/0000:09:00.1/sound/card0/input22
[    9.392553] input: HDA NVidia HDMI/DP,pcm=11 as /devices/pci0000:00/0000:00:03.1/0000:09:00.1/sound/card0/input23
[   22.099789] snd_hda_codec_hdmi hdaudioC0D0: HDMI: invalid ELD data byte 7

lspci -k | grep Audio -A4

returns:

09:00.1 Audio device: NVIDIA Corporation GP107GL High Definition Audio Controller (rev a1)
	Subsystem: Micro-Star International Co., Ltd. [MSI] GP107GL High Definition Audio Controller
	Kernel driver in use: snd_hda_intel
	Kernel modules: snd_hda_intel
0a:00.0 Non-Essential Instrumentation [1300]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Function
	Subsystem: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Function
--
0b:00.4 Audio device: Advanced Micro Devices, Inc. [AMD] Starship/Matisse HD Audio Controller
	Subsystem: Gigabyte Technology Co., Ltd Starship/Matisse HD Audio Controller
	Kernel driver in use: snd_hda_intel
	Kernel modules: snd_hda_intel

https://help.ubuntu.com/community/SoundTroubleshootingProcedure

https://answers.launchpad.net/ubuntu/+source/alsa-driver/+addquestion