First of all, I've never heard "the hum", but even if I had, I'd throw out isolated instances and keep only widespread reports for data points. But I know for a fact that Geophysical Research Letters doesn't mess around, so I think it's time to take this phenomenon seriously.
Ocean wave induced oscillations could be one component, but I guarantee that's not the only naturally occurring infrasound source. There is an entire bureau that monitors Earth's hydrological systems. It'd be interesting to try and correlate widely reported instances of "the hum" with certain atmospheric conditions. Local geometry and crustal properties are certainly another variable to consider. It's actually a pretty convoluted problem. I might check out the journal article when I'm on campus tomorrow (or I can buy it now for the low price of $38!). Hopefully there is actual mention of "the hum" in the published journal article.
Honestly, I didn't think that ocean swells drove a coherent oscillation in the atmosphere. An organized swell is more obvious somewhere like Teahupoo than on your typical U.S. beach. Still, it's hard for me to imagine the ocean-atmosphere system globally interacting with any sort of organization, even though it absolutely does. Where and when conditions could prevail to produce audible humming? Holy hell, it really isn't easy to tell yet. If we could take higher resolution length of day fluctuation measurements, fluctuations should correlate with global atmospheric and ocean oscillations...
I could go on and on, so I'll cut myself off here. Definitely an interesting aspect of planetary science.