I had one like that some years ago. Changed out a receptacle and after I turned the power back on, went to check the voltage. I was standing in front of the receptacle and I hear this hissing, sizzling sound. I go and turn the breaker back off, take off the receptacle cover plate, check the connections and the splices to make sure they're tight.

When I turn the power back on, I'm standing in front of the receptacle and I hear the sound again. I squat down and am looking at the energized receptacle to see if I see an arc anywhere, and I notice the sound doesn't seem to be coming from the receptacle at all. It's coming from my boot!

It turns out there was a space under the sole of my boot, when I put weight on my heels, it would compress the space and force air through the crack in the boot-tread, which made a very distinct hissing noise.

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-John