While diagnosing what I thought was a Windows Update failure, I discovered unrelated massive resource consumption and file scanning activity apparently tied to the Start screen in Windows 2012.
10 to 20% constant CPU usage by Windows Explorer.
Rapid file scanning or Shared Folder usage in the case of folder redirection.
Resource consumption begins immediately after opening the Start screen and performing a keyboard search.
Closing the Start screen does not help.
Sign out the current user. This action will shut down Windows Explorer, preventing the unwanted symptoms until triggered again by a user.