Masking the mains hum to improve anonymity Today, a news blurb appeared that claimed that attackers could identify the location in which an audio record was taken by matching the mains hum to known data. Sadly, I fear that this might be feasible. The mains hum has quite a tight tolerance, but any aberrations (that cannot be done away with) could be spotted easily. In fact, power suppliers have to observe the hum and adjust their stations accordingly.

How could you manipulate a record such that this information is destroyed completely, so that it is not reconstructible by any means? Filtering alone might leave enough remains to still perform that identification. After all, all filters have a finite number of poles.
I believe it's possible to get location information from 50/60 Hz hum, particularly if the recording is long-duration.  See this paper by Catalin Grigoras from 2009.

One way to defeat this would be to add enough sampling rate jitter to your recording so as to swamp the small variations in mains hum.  That paper showed information from variations of around 1 part in 1000, with sampling every 10 sec or so.  If you let the sampling rate of your signal drift around randomly on that kind of scale (which would have no perceptible effect), it would obscure the variations in the hum.  

So, for instance, if you let your sampling rate drift by +/- 0.1% (e.g., 44,050 to 44,150), with a maximum rate of change of, say, 1 Hz in 10 sec, that would impose a random component on top of the underlying power-grid-derived variations, making them hard to separate.  This modification would be completely inaudible.