High cpu usage after booting

[fred carno]

I am currently running Mint 18.3 initially installed with KDE, now usually run Xfce and have done so for a while without problems until a recent update. Now the cpu is racing away at an average of about 25%, this is shared over 6 processors. It has nothing running apart from the Xfce gui. Usually this would only average about 0.1 to 2% but it runs at 25% unless I run top which (without me doing anything else) seems to kill the offending processes and usage returns to normal, providing I don't shutdown top.

The offending processes have been:
systemd
gvfsd
systemctl

but not all at once, i, e, only one at once. (as reported by top)

Also it will behave itself if I don't login from the splash page but give Ctrl+Alt+F1 login from a terminal and give startx to start Xfce.
This behavior also happens with KDE.

Does anyone know why this is happening?