I'm experiencing very frequent (and regular) GUI pauses on my system.

Every 30 seconds (pretty much exactly) the GUI will freeze for maybe .25 to .5 seconds. The mouse stops moving, keys stop echoing and a stopwatch timer briefly pauses.

I'm using the Intel Graphics driver available from: https://download.01.org/gfx/ubuntu/13.04/main

I've looked in a few places and tried a few things for a solution:

• I've checked cron and anacron for scheduled processes.
• I've disabled background processes (eg mysql, postgres, apache) not that these were doing anything anyway

• I've checked the following posts and tried the suggestions there:

  Unity GUI pauses/freezes for less than a few seconds

  How to go about troubleshooting frequent system pauses

I've watched the system using top and System Monitor and there are no spikes (or even blips) of cpu usage when the pauses occur.

There are no obvious error messages in dmesg or syslog

There is loads of free RAM (8GB+) and no swap usage

If it helps it's a ZooStorm i5 laptop with a HD4000 GPU, 16GB Ram and an SSD.

Any help / suggestions would be very gratefully received.