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Invisible oscillation generally cannot be seen or heard. The One way you know you have it is that all throttle stick positions can act as if they were closer to the middle. Another way you know is if you have two FMS positions that use different PID banks (and manual thrust), and one set of PIDs has significantly lower D term and you are hovering and switch from the high D to the low D, you may notice that you need to add power to maintain altitude. Increased thrust from the high D term is caused by the ESCs being commanded up and down and being quicker when increasing RPM than when decreasing it. You may find that motors tend to run hotter and batteries don't last as long as they should. Powerful copters (those that require less than 50% power to hover) will take off with much less throttle than expected. Weak copters (those that require more than 50% power to hover) will need more power than expected to take off, or will not take off even at full power. Try reducing your D terms (Stabilization -> Advanced), or increasing (doubling) GyroTau (GCS -> Configuration -> Stabilization -> Expert -> Gyro Noise Filtering), but realize that increasing GyroTau will make AutoTune create very slow smooth PIDs.
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