We're trying to diagnose the cause of slowness on our Database server.

We're running the latest rev SQL Server 2005 on Windows 2008x64.

The behavior that we're seeing is this: We see the SYSTEM process spike one of the CPUs for about 2 minutes, during this time SQL server slows down by a factor of 10. The slowness lasts until SYSTEM is done, then in an hour everything starts again.

During these slowdowns disk writes don't spike, paging doesn't spike, the only noticeable precursor we see is that SYSTEM maxes out one of the sixteen (HT)CPUs.

Note that this doesn't happen at the top of the hour, it just happens once an hour, and it shifts a bit depending on the length of the incident.

At the moment this is causing intermittent slowdowns, but when the server is really busy it can cause Worker Thread starvation.

The server is a Dual Quad Dell R710 with 96GB of RAM and RAID10 data/log disks.

Has anyone experienced this kind of problem? Does anyone know where we should look?

Edit: SQL Server Version is 9.0.4035