The high pitched whistling sound comes from the air inlets in the wings.
Just because the audio track is so fine, but since we're talking about the Corsair, here's a cool pic I found.
|Marine Flyers of the Black Sheep Squadron Will Trade Zeros For Ball Caps|
Rectangular openings mounted in the wing leading edge at the fuselage junction supplied cooling air to twin oil coolers, one in each leading edge. Induction air was also taken from the leading edge air intakes, ducted to the first stage of the supercharger. Featuring an intercooler for the two-stage supercharger, cooling air was routed from the leading edge air intakes to the air-to-air intercooler. Flow splitters were an integral part of the air intakes due to the requirement of ducting the air 90 degrees as soon as it entered the air intake plenum. At high speed these flow splitters (six per side) emitted a loud whistling noise, which prompted the Japanese to call the F4U "Whistling Death."