This is an F540 running 5.2.1P2D14 The filer is basically doing nothing - but every 5 seconds or so the CPU goes up to 80 or 90% and stays there for 6 or 7 seconds.
have you tried doing a ps on the filer to see what actually was sucking up the CPU? you'll probably either want to do this via rsh piped to more or redirected to a file.
-steve