[Darryl Ramm]

I also noticed you have Dropbox running. So while plugins are still the first suspect, all these sorts of disk and remote backup utilities can cause problems, especially if you accidentally have content playing to/from a dropbox volume. So another thing to consider if nothing else works--check stuff is not playing from there, it's an easy mistake to make.

And a comment on Time Machine -- it's not a great primary way to back up your boot/system drive. A utility like Carbon Copy Cloner is a much better way for most of us to work, as it gives you instant boot recovery from problems using an external clone drive. Time Machine can be OK for backup of general user documents and maybe sessions.