Workstation 12 Sound when changing Guest between windowed and Fullscreen

Hi;

   I'm trying out Workstation 12 Pro. I've been using Workstation 11 on a Windows 7 Pro 64-bit host.

  I tried using a Windows 7 Pro 64 bit Guest which had been running hardware version 8 with Workstation 11. I updated it to hardware version 12, and installed the WS 12 Guest tools.

  I've noticed that now I hear a sound being generated (not sure if it's from the Host or Guest) when I change the Guest from Full-Screen to Windowed. ('Enter Full screen mode' and 'Exit Fullscreen mode').

  This didn't happen under Workstation 11.

  Is this new for WS 12, Is there a setting for this, or am I missing something obvious?

  Thanks.