I had the same issue but the fix others have posted didn't take care of the issue for me, even turning SMB off completely only delayed it. After turning everything I could and turning them back on one by one to see what caused the issue, I finally tracked it down to the Dynamix Cache Dirs plugin. Once uninstalled the drive and CPU use dropped to idle and have been there ever since. Hopefully this helps someone else out, at least it's another thing to try if the above fix doesn't work out for you.