As I replied to your first question back in September, you need to look at the command line to get the file name of the script being executed. That should help you trace the activity back to something.
Here's that command.
Get-WmiObject Win32_Process -Filter "name = 'powershell.exe'" | select commandline
Another user had a problem with Powershell activity and I wrote a little monitor script for him. Run that and post back what it finds.
I do not recommend disabling Powershell.