Tail vibration on R60
 

My brother and I were out flying the raptors today and just when we were about to pack it up I noticed quite a vibration on my R60 tail that my brother had been hovering. It's not visible but you can feel it. It's strong enough to cause the main and tail blades to "drop" (upper tail blade will drop down, main blades will move a bit from center) when it's on idle. Once the heli spins up it's solid. No wobbles or vibrations (except the one caused by training gear at certain rpm but that passes quicky). I haven't noticed this myself before but on the other hand I never used training gear myself on the R60 (my brother was doing his 1st hover :) that's why we had the training gear on). The engine is running quite rich due to being broken in. I know this can cause vibrations or could it be the normal vibration of the engine amplified by the training gear and hard surface (concrete). Didn't have time to check it w/o the training gear today and I haven't noticed this before. Any insights on this ? (oh forgot to add, it's a new heli bout 2 hrs flight time on it and it was a ARF kit)