Audio sharing not allowed

[jaccolo]

When running 'vagrant up' with Ubuntu 18.04 + Vagrant 2.2.7 + Vbox 6.1.2 the following error appears when vagrant tries to start the second VM:

There was an error while executing `VBoxManage`, a CLI used by Vagrant
for controlling VirtualBox. The command and stderr is shown below.

Command: ["startvm", "f890dcc2-4e56-4533-9ac8-f56ce46b8a36", "--type", "headless"]

Stderr: VBoxManage: error: Failed to construct device 'ichac97' instance #0 (VERR_CFGM_NOT_ENOUGH_SPACE)
VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005), component ConsoleWrap, interface IConsole

This issue can be solved by entering a line that disables audio:

$ git diff Vagrantfile
diff --git a/Vagrantfile b/Vagrantfile
index e6b8370..aeba60d 100644
--- a/Vagrantfile
+++ b/Vagrantfile
@@ -6,6 +6,7 @@ Vagrant.configure("2") do |config|
 
   config.vm.provider "virtualbox" do |vb|
     vb.memory = "512"
+    vb.customize ["modifyvm", :id, "--audio", "none"]
   end
 
   # must be at the top
@@ -39,4 +40,4 @@ Vagrant.configure("2") do |config|
     end
   end
 
-end
\ No newline at end of file
+end

Unfortunately I have no permission at this repository to open a pull-request.