Constant CPU and Disk Activity

I just upgraded my MBP from Tiger to Leopard, and also upgraded from trial to full .Mac account, so I now have an iDisk for the first time.
I have iStat Menus installed and where, before the upgrades, the CPU graph showed a very low level of activity (almost zero) when the computer was idle, it now looks like a picket fence, with spikes reaching almost to the top of the graph. The disk activity graph exactly matches the CPU graph with regular spikes, which occur about very 7-8 seconds.
I opened Activity Monitor, and the highest usage switches between 'Sync Server' (with a value of anything from 2 to 9) and 'kernel-task' (with a value of around 2.5). Something called 'mds' sometimes pops up to the top (with values of 2-3). It appears the culprit is 'Sync Server'. I've tried iDisk sync set to 'Manually', and also with it turned off altogether, but it makes no difference.
Does anyone know what's going on here and, more importantly, how to get my MBP to relax again.
Thanks in advance,
Steve = : ^ )

I'm resurrecting this question because the problem still exists. Restarting the computer always stops the spikes but they always start up again at some point (I'm yet to pinpoint a cause) and, once happening, I can quit all running apps (except Finder) and they persist, and they seem to occur about 10 secs. apart.
The spikes occur in both cores but, if one core has a big spike (close to 100%) the other's is small and vice versa. Or they both have moderate spikes. It seems the total usage is about the same for every spike, though spread differently between the two cores.
And the HD still shows activity at the same rate as the spikes.
Any ideas what I should look for?
Thanks in advance,
Steve = : ^ )
Message was edited by: Steve_Ball

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