It's high enough frequency not to notice at all unless you wave it infront of your eyes really fast while looking at the head in the dark, even then hardly so. I haven't had issues with it being audible either, though on 14500 I can hear it if I hold it to my ear. I know inductor whine can cause the whining noise (PWM itself is neither necessary nor sufficient to guarantee a whine) but PWM switching of different frequencies is certainly responsible for whining on some lights, no question about it. On my iTP A3 3 mode the freq is so low on low mode I can almost distiguish it as individual click click noises, just very fast, on med it's more of a traditional whine, like a very quiet chaingun actually! On high there is no whine as it doesn't use PWM. This same pattern but at higher relative frequencies is apparent on most of my 7135 linear driver based drop-ins to varying degrees. This does not however mean that all lights using PWM will whine, only some. It's usually correlated with the power going through also, (the iTP A3 is much loader on 10440 than ni-mh) so a light with low output like the Mini AA you would be unlucky to find audible PWM.
On a side note, if you have any PWM based lights and can't hear the whine, try switching it on while pointing it closely at a black or dark fabric. This somehow amplifies the audible whine, a massive amount in some cases.
Also, if you have a light that whines but aren't sure why, then try the same thing. The amplification should only work for whines caused by PWM switching and not ones caused by an inductor.
