This is a bug I've run across on HP Probook 6XXX, 6XX, 8XX and HP Elitebook 8XXX, 9XXX, 8XX, and 1XXX laptops. This is mostly an annoyance and usually the volume works, the mute button works, but the orange "mute" indicator light is stuck on orange.
If you look through HP forums, you will see HP Support claim this is a BIOS issue. I've run across this issue several dozen times and each time I do a fresh installation of Windows on the machine.
The problem is usually caused when Windows Update installs the Audio Driver during the OS Install Process. Windows Update will install a generic driver that works fine for the audio, but does nothing to control the mute indicator light.
The solution is to download the actual HP driver from the HP Diver Support site. If you are installing Windows 10 on the machine, you will need to download the Windows 8 or Windows 7 driver. While the installation process claims you will need to the reboot the computer after the driver install but this is not always necessary.
In Windows 10, you can use the Windows 8 driver. Upon completion of the install, the light changes white immediately.
HP Elitebook 8470P
Windows 8/10 64bit: Use IDT High Definition (HD) Audio Driver SP63916.exe
Windows 7 64bit: Use IDT High Definition (HD) Audio Driver SP60317.exe
For some models, there are no Windows 8 or 10 drivers available. You can use the Windows 7 drivers instead.