I hope this isn't it. Usually, it's just a program (or part of one) going rogue. A couple older versions of MacOS had an issue with the Push and Sync APIs with cloud services. They were patched out at a later date, thank goodness. Many times, a simple restart would fix the services, because it would quit them normally, then restart.
Unfortunately, there was a bug in a couple older versions where that service wouldn't right itself. Basically, it would sync, but not get part of the data, so it would re-search for the sync (to complete it), get it, but NOT register that it got it. So it would redo that process over and over, eating up processor speed (and battery on notebooks).
Good news is that it is really rare, and keeping up to date/patching normally fixes it. I'm thinking with yours, it's just a rogue service being stupid.