Process (fmfd) spamming my console with sandbox denies
I just found how to solve this problem.


Go to the /System/Library/Sandbox/Profiles folder, you will find a file named fmfd.sb. You can't modify it here, so copy it to your desktop.
Open the copy with TextEdit, locate the allow file-read-metadata section and add a new line under (literal "/Volumes") for the folder that can't be read, for you that should be (literal "/Volumes/Macintosh HD").
Replace the original with the copy (don't forget to make a backup), since it's in a system folder it will ask for your password.
Reboot your Mac the error messages in Console should be gone!