Hi,
I have been struggling with a windows guest OS freezing for 1 - 2 seconds every 20 - 30 seconds and could find nothing helpful by googling. Pinging the VM from outside the environment showed that every 25 or so seconds a packet would be lost and this coincided with the freeze in the guest OS. After much playing around with anti-virus, disk types, cores and many other things I finally discovered that un-ticking the "Connect at power on" for the Floppy Disk resolved the issue completely (I have no floppy in the hosts system)!
Hopefully this will save someone else feeling like they are hitting their head on a brick wall when doing with a Google search in future 
Steve