Very short rotors-span . . .
The main rotor of the old UH-1H Iroquois (AKA, "Huey") gunship runs at 324 rpm.
In comparison, the far less air pressure on Mars requires a different thought. The Mars helicopter will do 1,900 to 2,800 rpm with the blade-tips hitting greater than 0.7 Mach.
Even with the lesser atmosphere I would image a very high-pitched whine when in flight.