Actually whistle is more of a cinamatic effect. The pilot hears and feels the bomb release mechanism. Unless the aircraft is at zero g's when the bomb is dropped, it jumps up slightly as the weight of the bombs is relieved from the attach points. Movies have conditioned us to expect a whistle. Its likely that any whistle from the arming mechanism spinning off in the first few feet of free fall would be lost over the engine, wind noise, and the pilots helmet/headset combination.
MiG
Going to use release sound on my system Mitsu. Thanks!