>I have noticed that my SQL Server 2008 (Express) uses CPU cycles when nothing is happening on the database. At first I thought it was doing some housekeeping with idle CPU time -- it was using anywhere from 2% to 35% of the CPU (with usage increasing the longer the system was otherwise idle.) So, I paused the SQL server and the various services (reporting, browsing, etc.) It was STILL chewing up CPU. This goes on until I stop the service alltogether -- that's when CPU usage finally returns to zero.
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>This is pretty annoying, because even at 2% usage my system becomes sluggish (must be some serious I/O going on in the background?)
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>The server is installed on my desktop machine (dual core AMD with 4 GB of memory.)
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>Any ideas?

Try asking here http://social.msdn.microsoft.com/Forums/en-US/sqldatabaseengine/threads - you have better chance of getting expert's advice.