Found it ! AVG Antivirus Free needing to install a driver for something, the driver unsigned ! Deleted AVG Free, cleaned the registry, tried to reinstall AVG Free and it would not install untill I allowed that driver to be installed as well. Allowed it to install, AVG Free completed the install and there has been no recurrence.
As a side note though, AVG Free still occasionally finds Trojans which Malwarebytes and SuperAntiSpyware do not find. Is is possible that AVG is finding false positives ? Anyone come across this before ?