Allegedly, on or about 04 March 2016, Richard Ibbotson sent:
Switched off some plugins. I think that's done it.
Try re-enabling, one by one, to narrow it down. I think you need to, to ensure that you don't have a compromised system.
It could be something as simple as a plug-in looking for an update for itself. Or one of those filter plug-ins that looks for whitelists and/or blacklists. It could be something as annoying as a plug-in calling home to mummy. It could be something trying to complete a download that didn't quite finish, or did finish but didn't seem to.
As you can see, there's any number of things that could cause that effect, and you really want do know whether it's benign, or not.