Here's my 2p worth as an ex-RR acoustics engineer.
At take-off the fan tips are supersonic - typically Mach 1.4 - and generate shock waves. Normally fan related noise is heard at the fan blade passing frequency (Number of blades times RPM/60) and harmonics of this.
With shock related noise however the non-linear propagation of shock waves compound with small blade to blade differences and the spacing of the pulses becomes irregular.
The sound that this makes is usually referred to as "Buzz-saw" noise.
This has noise at all harmonics of the shaft frequency (rpm/60) peaking around 1KHz.
The low frequencies are also not easily attenuated by the acoustic lining of the nacelle.
The peak radiation of this noise is about 60 degrees to the intake axis but often appears to be higher because the aircraft has moved forward in the time it takes to propagate.
This is rarely a problem on approach unless you use more than about 65-70% N1.
Oh - and the whining noise at low powers is probably blade interaction noise from the LP turbine or compressor.
[This message has been edited by Mark 1 (edited 26 October 2000).]