It took me less than an hour to make the top of the Calf Top G/NP-022. The forecast said cold NW winds at about 25 - 35 mph, with showers, some heavy.
At the top It was quite warm and a light wind came from the SW. The tumbled wall provided more than adequate shelter.
As I stood next to the Trig point, I wondered what that strange humming noise, “mmmmmmmmm…” was. It sounded like it might come from some kind of electrical motor or power supply. Some motorised devise hidden near the trig point by the OS? A navigation device? .
In the meantime, I looked for the device. Nothing in the fallen wall. Nothing near the wall and no sign of any ground disturbance either. ??? Listening closer, the sound was not coming from within the rocks. I could hear it resonating/humming through a timber support wedged against the new wire fence, Ahh! getting closer! It wasn’t coming from the concrete trig point either. Then as I pressed my ear against the new fence… Eureka the low humming was coming from the fence. Not all of the length of fence but just around the summit area and several yards along the fence both ways. The noise didn’t quite disappear when I tried to press or alter the fence either.
I’ve been climbing hills and mountains for over 60 years and only once before have I heard a sound I couldn’t recognise, and that was on a traverse of the Five Sisters of Kinsale, Scotland in a wet winter storm. That noise sounded like air escaping from some kind of bottle of fizzy drink. But i wasn’t carrying any though. Could it be air escaping from my empty water bottle in my rucksack and caused by a drop in air pressure. Nope. I’d taken by rucksack of and checked the contents. I suspected it might be some sort of electrical noise due to atmospheric disturbance and hoped I didn’t get struck by lightning.
Here’s my office, and here’s the fence. Brand new, and very shiny, and the wire is held on by a type of clip I’ve never seen before which allows the wire to move freely along the whole of the fence length which must have been hundreds of metres or yards long and under very high tension.
An hour or so later I packed up. The wind may have dropped very slightly and the sound had stopped.
I’ve heard that in the past on Tinto Hill GM/SS-064. It was near the bottom where there was long runs of fence wire no longer clipped to the fence posts that was vibrating in the wind.
Its the noise of an approaching, and incredibly rare since they decimated their food supply, Rubberius Thevious.
They survive by eating the rubber bungs from fishing poles. Whilst rarely seen and never photographed, they have learned to stalk SOTA activators in search of food.
Whilst not inherently dangerous to humans, they do cause discomfort when your fishing pole suddenly extends from your backpack while on a steep descent.
I now always carry several spare bungs in a sealed lead (2 inch thick walls) container up every summit. It seems to work since from the time i started doing that, i havent had any issues with these beasties.
We used to hear that often in open country when “open wire” telephone lines ran for miles across the land.
I was probably in the last cohort of apprentices taught how to put them up and “regulate” the tension so that all the wires between poles had the same sag, and looked tidy. I digress!
I have also heard my linked dipole singing in the wind occasionally…
Certainly heard that from wind on fencelines many times.
More worryingly the section of our 7-wire boundary fence that passes under the national grid power lines humms no matter the wind conditions. I note that someone has installed electric fence insulators at either end of this section. Never had the courage to touch it to find out if it really is acting as the 2nd half of a transformer!
I suspect that this was Karman Vortex Shedding. I have been fascinated by this since first learning about it at University. Sometimes you see spiral projections from the top of circular towers to prevent this phenomena.
It’s a shame the fence had metal posts rather than wood (which would possibly have suppressed the humming) as otherwise, that could have made a rather nice antenna if you could match your radio to it!
73 Ed.
I remember in the late 1950s, as an 8 yr old, getting out of dad’s car whilst we were visiting someone’s house in the flat plain that is much of arable Norfolk. Like you said, the telegraph wires which ran alongside the road, were ‘singing’ with the wind.
As a young engineer, I worked on a large chemical plant producing about 1 million tonnes per year of ‘aromatics’ - benzene, toluene, xylenes and so forth.
The individual chemicals were separated out by a process of distillation involving large, tall, towers. Because xylene and ethylbenzene have similar boiling points, you require a huge tower to effect the separation. Physically, we had TWO 300ft-tall towers, side-by-side, to do the job.
Just as you note, there was metal spiralling on the outside of the top (20 percent?) of each tower to manage the vortex-shedding issue.
Elsewhere, I worked on a new plant which had tall (80-100ft) metal chimneys on the 20 or so pyrolysis furnaces. At the outset, these had NO vortex-shedding arrangements. After a few months operation, cracks started to appear in the metal transition joints between the base of each chimney and the body of the furnace. The whole unit had to be shutdown for some months to fit vortex-shedding fins on the chimneys; extremely expensive
Listening closer, the sound was not coming from within the rocks. I could hear it resonating/humming through a timber support wedged against the new wire fence, Ahh! getting closer! 
the low humming was coming from the fence. Not all of the length of fence but just around the summit area and several yards along the fence both ways. The noise didn’t quite disappear when I tried to press or alter the fence either. 
