Just a thought: On the Flight Control board, do you have either Velcro or foam over the aperture on the pressure sensor to act as a gust filter? Andy.
Oh well, there goes that theory. At least that related to differences that might be caused when it was windy and there was a dome on the copter... So what is causing that shrieking sound, I wonder? Andy.
One thing I found wrong with my machine recently was that the screws holding a propeller mount to its motor had become a little loose. It caused the motor to make a squealing sound. So you might want to check that.
Thanks for the hint regarding the propellers, realy were a bit loos. Vibrations stll there. But: found that setting the radians to 140 roll and 180 tilt changed it a bit. Still dont get the point with the height sensor and the vibration though. i never fly with the height sensor active, so it should not affect the fc output or did I get it wrong?