I had the System Monitor running in the Dock while doing some CLI work, and I noticed that all four CPU cores were running while I was not doing anything with the system. I opened SM up and found that launchd, UserEventAgent, and mds_stores were hard at work doing something-or-other. I am not running TM, and had nothing else of my own running in background, it was just El Cap twiddling it's thumbs (to be polite). I stopped everything that was active/asleep on the Dock, with no change to the situation (the screen shot was after I'd done this). A reboot fixed the problem (for now), but I see other complaints here and there on the Intertubes about this, but no real answers other than "known bug, file bug report just in case" (from last Fall). Any others seeing this?