Why do flying wires hum louder in a sideslip?
Here is one reason.
It once was common for suspension wires to be flattened rather than circular in cross-section, to reduce drag. those wires were then aligned with the airflow past the wing and fuselage in cruise. However, any time that airflow was not aligned with the wires, they would present an angle of attack to the slipstream and generate lift, which would pull them out of position, stretch the wires, and twist them to increase the local AoA. Then the wires would shed a vortex, stall (killing the lift), untwist, snap back, and then get pulled out of position again, etc., etc. and the result was the wires would &quot;sing&quot;.
You can think of this as a special case of aerodynamic flutter.