svchost consuming CPU after boot

I had posted this topic in the Windows Update forum and it was suggected I
try posting it here, after trying a number of things suggested. Here is the
post:

I've read many posts regarding the lengthy start-up issues associated with
svchost and MS updates - mine appears somewhat different. After booting up,
and after all services have started, my machine runs through cycles of CPU -
viewed on Task Manager these spkies are typically around 40% of CPU,
sometimes higher, and are occurring on a very consistent cycle, around every
6-8 seconds. This happens even with nothing open on my machine.

I've run all the scans to check for viruses and spyware. I can see that
these processes running are within svchost.exe and/or services.exe. I've
tried shutting down everything that is in my startup and the problem still
exists. This cycling of CPU goes on non-stop, all the time. As it eats CPU
on these cycles, other processes are now affected - example, a full virus
scan now takes about twice as long as it used to. As there are tons of tasks
running within svchost, I have no idea how to narrow this down. I'm running
XP Home/SP2 and have applied all updates automatically. Any ideas?