Here's something I just discovered thanks to Earl Gray and others. Been fighting the "micro-vibration" thing for a while, done the ribbon cable, etc, etc. Started reading about motor balancing and asked how to use MP to run each motor by itself. Well, turns out not only is it a sweet function, it's simple and easy too! So, I'm just running each motor and #4 motor is SCREAMING like a shaking coffee can full of nails! Definitely a bearing that would leave me to believe it wouldn't have made it through one more flight. So, it's not the ultimate "is it going to break and when" solution but in this case I'm sure I avoided what would have been an inevitable loss. SOLO, MP, and Tower continue to amaze me at the richness of their capabilities. Run the motor test yourselves, I think you'll be surprised at what you hear.