Symptoms:
Attempting to vMotion a virtual machine fails with the error: Device 'HD audio ' has a backing type that is not supported

VMware vSphere ESXi 6.5
VMware vSphere ESXi 7.0.0
VMware vSphere ESXi 6.7

HD Audio devices are not supported on ESXi virtual machines and are not available as devices to add via the vSphere Client.

There is no resolution. 

Disallowing vMotion when the audio device is currently connected is by design. 
To perform migration either the device needs to be disconnected or perform a cold migration.

Workaround:
To workaround this issue you need to manually remove the HD Audio device by editing the vmx file of the VM. 
 

• Power off the VM
• SSH to the ESXi where the VM is registered
• Make a backup of the VMX file by copying it to another location
• Remove audio-device from .vmx-file: 

          # cd /vmfs/volumes/datastore
          # vi <path-to-vm>\VMname.vmx

• Delete lines:

        sound.autoDetect = "TRUE"
        sound.virtualDev = "hdaudio"
        sound.fileName = "-1"
        sound.present = "TRUE"
        sound.pciSlotNumber = "35"

• Find the vmid for the affected VM:   #vim-cmd vmsvc/getallvms
• Reload configuration for the VM:     #vim-cmd vmsvc/reload <Vmid-of-VM>
• Power on the VM and attempt the migration again

Note: if you are unable to access via SSH, you may use the vSphere Client to access the VM's datastore and download the corresponding .vmx file. Once downloaded, use a text editor to make the above adjustments and then reupload the .vmx file with the changes into the datastore.

* Tips for editing a .vmx file (1714)

* Reloading a vmx file without removing the virtual machine from inventory (1026043)