I still have no clue what is causing this, but I am pretty clueless when
it comes to Windows PCs anyway, and as you might have guessed: The PCs
making these connections are windows machines.
Continuing our off-list discussion for this on-list comment...
Without a reboot, try to connect the outgoing connections to a process.
I believe sysinternals have some tools that may help with this.
Gadi.