You didn't say which FAQ you checked, which steps you followed and what results were (if any, maybe none). I'm thinking particularly reltaing to process explorer/monitor steps described in what I think might be the more relevant FAQ: General slowdown or instability investigation steps
Some of the suggestions there might seem impractical (about eliminating possible contributing pieces, shell extensions, etc), but on the other hand it also depends how frequently it happens. If once every day, it shouldn't be too burdensome to turn lots of things off to see if there's a change in behavior.
unfortunately, without a crash dump being generated... not sure if anyone will be able to provide any more prescriptive steps to try ;-(.