First of all, I definitely do not claim to be an authority on Phantoms. I'm still learning and have a long way to go before I feel like an "expert". But I've been flying RC for over 40 years and have picked a few fairly good habits over that time. Like most people, I have an ever growing library of videos I've captured with various Phantoms and non DJI UAV's. Playing back a video I took today, I noticed that I seem to hear more resonance when flying than earlier flights. So I went back and pulled up some video from some flights of several months ago and sure enough.....they were much quieter and smoother with no resonance and no jello. By listening to the difference in the sound of the Phantom now and then, I can tell that something is changing. Now I have to investigate to find out exactly what. Another thing that has tipped me to some kind of developing potential problem is that I'm beginning to get Jello in my videos. I did not have ANY jello in my videos until the last 10 flights or so and it seems to be progressing. My initial suspicion is either propeller imbalance, motor wear, stress cracks or the controllers aren't controlling the motors as accurately as they used to. Propeller imbalance seems the first logical thing to check because that would be the most likely thing to change and easiest to determine. I have used prop guards on this puppy since day one. They all look perfect by the way but I'm going to remove them and do a magnified view to make sure none are developing hidden cracks. Balancing is definitely in order. A prop that develops a crack at the hub could potentially hang in there for a while...but cause some resonance like I'm hearing. Stop flying. Remove props and find out. Motor wear: seems unlikely since I only have 40 flights or so on this Phantom. But I'm going to check them for shaft freeplay, vertical shaft movement and any other potential developing problem as best as I can. Perhaps they need a little lubrication. Maybe a bearing has worn. Better to check than lose a bird. Stress Cracks: I have used propeller guards on this particular Phantom since day one. I don't see any cracks anywhere in the shell and I've heard that prop guards reinforce the shell under the motors but because of this vibration / resonance I'm going to remove them and examine the shell carefully. ESC Controllers: The controller boards control the speed of each motor. While I can't see how a controller board would cause this issue...I'm just keeping it in mind. I don't know of any way to determine if there's any developing issues with a controller board. Well...maybe if one controller board is pushing one motor too fast it could cause a resonance? You tell me. I'll post back anything I find but I guess my point is that sometimes problems that eventually bring a Phantom down might be avoided through careful maintenance and paying close attention to the signs that something is changing. YMMV It would be interesting to hear if some of you guys have experienced these kinds of changes and if you took action or if you ignored it and subsequently had a crash or other issues.