Hi,
Since yesterday I've been trying to get rid of a annoying tbe on my cx3.
I checked everything many times and changed all blades and flybar just in case, with no result.
I put the originals back and checked John Salt's web site to find an answer for what was going on.
He emphasizes that not only the flybar must be completely loose, but also the upper blades must seesaw loose on their pinions.
I really don't know what I did after that, but the tbe is gone for now.
It appeared just like yours: all of a sudden and with not apparent reason.
And it went away just the way it came.
Go figure.