Open Users & Groups in System Preferences and see if there are any processes in the Login Items, see if there is one you uninstalled but remains there.
There are other places to look, for instance have a look in Activity Monitor and see if there are unknown ones to you.
Last, look in the /Library/LaunchDeamons/Agents for unknown processes which load at startup
Thanks for the reply. There is a long list of things in Activity Monitor that are unknown to me (need a tutorial !) there needs to be an Apple Official Logo in the list to stop me killing critical activities e.g.
I'll have a trawl through Agents and see what transpires.
Yes, agree, there are many processes in Activity Monitor, I know most of them so I know what I do, you can't really break the OS by stopping a process but you could stop a process which makes the OS stop, for instance, if you stop loginWindow you are instantly logged out.
If it comes back reply to this post and I will try to see which app or process it was.