that annoying sound is yet again evidence of Apple's engineers thinking different... that sound is called 'white noise' because it is EVERY audible frequency all at once... this is a STANDARD in the audio industry and is commonly used in RT60 frequency spectrum analysis, like what a sound engineer does in a rock'n roll venue to equalize his audio output according to the room's acoustics which are measured by amplified white noise to the PA loudspeakers in a theater (for example) while 'listening' to this sound thru a microphone that is hooked up to a spectrum analyzer.
That said, it MAY be 'pink noise' that Apple is using to accomplish this.
NO JOKE: these noises are SCIENTIFIC even if they have funny names like 'white' and 'pink'