My Raptor 60 w/OS70 has a tail issue. First flight is fine for about 4-5 minutes then the tail sort of pulses when hovering. Until then the tail is rock solid. I have swapped gyros ( from a JR 500t to a 401 & back), swapped tail servos (both digital), & yes the gyros were set to high speed servos. The drive train has no visible issues & minimal slop. I am beginning to think that the engine is causing the problem. There seems to be a slight change in tone. Mixture is good (lots of power & cool rear case). Running Cool Power 30% heli. Could worn ball link balls be causing this?