plasma-desktop cpu usage

[Brian Wootton]

I have been plagued for some time by odd hiccups in
applications starting or failing to initialise properly,
sometimes freezing for a short while before carry-
ing on. Cups and xsane have both failed to find printers
and scanners occasionally. I have to have more than one
attempt to 'get mail' from my ISP. I get the raspberry
from firefox every now and then and I have to retry, etc'
it's annoying without being lethal.
  I've found that System Monitor>System Load is showing
about 10% mean cpu usage, but with spikes up to 100%
at exactly 10 second intervals lasting about 2 seconds.
I have shut down as many apps as I can, but still it persists.
  What clears the load problem is to 'pause' plasma-desktop
in System Monitor>Process Table, it completely gets rid of
the spike! but, of course, I can't change plasmas or click
on icons until I click 'continue' again.
  htop shows plasma-desktop at randomly highish cpu levels
but never as high as 100%.
System Monitor>Load Table shows memory at 0.86 GB
with absolutely no change over time, with or without the
spikes.
  My question is, do I have to live with this? or is there some
way I can get a little closer to what's causing it? the fixed 10
second interval looks like a clue - but to what?
  Any clues or pointers would be much appreciated.
brian