Today it was the 2nd time the H gave a sound (same as the start up sound) but continously until I switched off the ST16...Purple flash and sats ok. Tried three times, same problem. took out the ST16 and H batteri and started all over....same continously sound. Checked Angel mode of course... took a few steps away from the H and started the motors despite the terrible sound, and the sound stopped... Then everything worked fine. What was the issue? Any clue? Scary as it was the second time in three month...