Most VFD's take an 3 ph input, convert to DC, and then convert back to AC by Modulating the Pulse Width of the Voltage Wave. The output voltage waveform looks like a series of high frequency voltage spikes. The carrier frequency of the output section firings is in most VFD's selectable by changing a parameter named something like 'carrier frequency' or 'motor noise'. there will be a distinctly different noise (pitch) at different carrier frequencies. The change in pitch is the result of the commutation frequency of the applied voltage. all the IGBT output section can achieve (in a normal VFD) is to switch the DC link voltage (700VDC or so) on and off in varying pulse widths necessary to emulate a sine wave.
The current waveform is reasonably 'clean' since the inductance of the motor serves as a current choke.
Most VFD output phase rotation is determined by the software alone, not the input phase rotation. Output phase rotation is almost always reversable in the software parameter settings.
Many VFD's are capable of receiving 1 ph input (2 phases of a 3 ph system), and sucessfully operating at about 1/2 rated KVA, since the absence of one phase simply derates the rectifier section KVA Output, which is the input to the DC link. I have seen VFD's which care which line terminals the 1 ph input is connected to. There may be others which do not.
Utility power is equivalent to a very low carrier frequency (no switching at all), and therefore the motor sounds 'normal'.
