That was my first thought ...while standing out there checking the video a few seconds after shooting. But it was confusing me, because there was no motorbike

That was my first thought ...while standing out there checking the video a few seconds after shooting. But it was confusing me, because there was no motorbike. I'd been trying to shoot without car noise, so I was facing the road, and (mostly) waiting for any vehicles to pass. When cars pass you can hear the loud wind/wheels hiss in this vid. I noticed that weird hum even in my tiny camera speaker. Later I checked for it indoors, and still there. I suppose I should check the frequency. If not right at 60/120Hz, and has doppler of moving vehicle, then it's much more likely to be a bike(etc.) that I'd not noticed down the road, and then my brain had edited out while I was talking. Finally, there's a power line about 20ft up on the other side of the street. Huge current surge? The usual b-field from that thing is so strong that any small pickup coil in my house will detect it, and for sensitive work I have to go to the back of the kitchen, over 100ft distant.