Mysterious night-time pulsing sound

Over the last few months, I’ve occasionally heard a strange sound coming in through my open window at night. It’s a distant electronic pulsing sound which comes and goes on the wind. It seems to be coming from the north of Edinburgh around Leith. It’s quiet, but distinct. I decided to record it. The resulting recording is a bit shoddy, but it does the job.

Leith Night Pulse

I’ve no real idea what could be making this sound. Any suggestions would be welcome. It sounds to me like an alarm or an alert, like it has been designed to sound as it does. I tend to hear it around 1-3 am. Given the direction it’s coming from, it could be something happening on Leith docks or something going on at the nearby sewage works. It might even be something happening on the large cargo ships and oil tankers which often sit out in the Firth of Forth. I live maybe a mile from the coast; the way it drifts on the wind suggests that the sound source is quite far off.

Some technical details about the recording

This was a bit of a hard one because the pulsing sound was very quiet and I wanted to document it to make it clearly audible. So the approach I took was to focus on and magnify the pulsing sound at the expense of an accurate recording of the general ambience.

As it was so late at night, the ambient sound level was pretty low anyway. To get a decent level, I had to turn up the gain on my Sound Devices 702 to maximum. To reduce the effect of noise from my flat and the building, I stuck the mic (my Rode NT4 in a Rycote full modular windshield) out of the kitchen window on a fully-extended mic stand. A boom pole would have been better but I didn’t have one. I turned off the freezer in the kitchen as with the gain so high the mic was picking up a lot of the hum from that. The hum was probably louder than the pulsing sound itself. I tried to stay completely still – with the gain so high, even the tiniest sounds could be picked up. Even though I was careful, there are lots of extraneous noises in there. Little floorboard creaks, doors closing elsewhere in the building.

Annoyingly, after a few minutes the battery on my 702 died and I had neither my spare battery nor the power supply to hand. I switched to a Tascam DR100 recorder, but the preamps on that aren’t as good.

Afterwards, working with the SD702 recording, it was very quiet so I normalised it. This made the pulse louder but of course also brought up the level of all the stuff I didn’t want as well, like bass rumble and hiss. So I then did some pretty strong EQ work to remove noise at the low and high ends of the frequency spectrum. I also slightly boosted the main frequency of the pulse to bring it out of the mix a bit more. The process was very rough and ready and not at all audiophile really, but it got the result I wanted: the pulse is now clearly audible, whereas insitu it was very quiet, only just detectable over the background noise.

If this sound keeps happening, I might try a few more recordings on still nights, hopefully with a bit more care and preparation..

17 Replies to “Mysterious night-time pulsing sound”

  1. Hey there I’m hearing a very similar sound at around the same time frame of between 1 – 4am. I began hearing this noise as early as September 2010 but it was much quieter back then and I didn’t pay too much attention to it. The annoying this is it’s a very quiet sound as you said but also loud at the same time if that makes sense. It’s very distracting. I also heard this sound at work in the day time for a couple of weeks, my colleagues heard it too but then it disappeared… I will try to make a recording of it but I live in central London near Farringdon so it’s very very noisy where I’m located yet I can still hear this sound. It’s a high pitched sound that comes in short pulses with every pulse becoming louder before eventually disappearing.

  2. My daughter and I just heard it in New york at around 1:30 am. It lasted around 30 seconds and was repeated twice. It was a sound but a vibration as well. It went deep into your ears and you feel it in your chest.

  3. Interesting…

    Further news on my drone is that a while ago I too heard the sound during the daytime. So I suspect the reason for hearing it at night was probably just low levels of other sounds – traffic etc – rather than it being a nocturnal sound per se. As it was daytime, I took the opportunity to call the nearby sewage works to find out if it might be coming from there. They said they were having construction work done and the sound might be coming from the construction machines. They said it would stop in a few weeks when construction ceased. Well, I’ve not heard the sound for some time now, so this explanation seems reasonable. Could your drone be related to construction work too?

  4. Thanks for the comment. It sounds like our experiences are quite different though. When I have heard this sound, it has been extremely quiet – subjectively, the loudness is comparable to, say, the ticking of a watch or the hum of a fridge. I certainly didn’t feel it in my chest. For that, it would have needed to be much much louder and also lower in frequency.

  5. I live in a block of flats, there are 3 floors and i live on the ground floor..My location is Sutton Surrey UK…
    I have this pulsating humming noise penetrating my flat every day and night, i seem to be the only one that can hear it, my partner cannot hear it and several tenants were i live cannot hear it.
    I hear it in the bathroom, i hear it in the kitchen, i hear it in the bedroom, i hear it in the lounge, i live in a studio flat so you can imagine how small it is..
    This hum is coming from outside and not in the block of flats, it is possibly underground somewhere?.Either way it is very annoying, i have my tower fan on when retiring to bed, even in the winter..
    Someone somewhere knows what this is and is not coming clean,,,shame on them, what goes around comes around…

  6. Feel sure what I hear and see in the Thames, Canary Wharf is the same. I have tried to look it up. It is a deep throbbing sound which wakes me so deep and throbbing it feels like it is penetrating everything with it’s sound waves including me. When I get out of bed (it happens at 3am in the morning) there is usually something like a very large tug boat, moving very slowly, and the water is very disrupted nut in a deep movement (not splashy) it makes me think it is actually a submarine. . Can anyone help? 22 July 2016 was last time I heard and felt it at 3am…

  7. This is just a guess, but based on what you say it’s possible that you’re more sensitive to low frequency sound than many people. In your case, the sound is probably made by the tugboat engines. Low frequency sound, or infrasound, can travel very far and penetrate through matter more effectively than higher frequencies, so it would not surprise me if the sound really is going right through your body as you suggest. There are many sources of infrasound, both natural and human-made, and most people don’t hear this stuff or just tune it out most of the time. But some people become particularly sensitive to it, e.g. the clusters of people who report hearing a hum in certain locations, such as Largs in Scotland.

    Some people at Salford did research on this issue, led by Andy Moorhouse. You might like to look at http://www.salford.ac.uk/computing-science-engineering/research/acoustics/psychoacoustics/low-frequency-noise

    Low frequency noise is difficult to physically block out, because it passes through stuff. If it is causing you trouble, my suggestion would be to try and change your own response to it, if you can. Easier said than done of course. What sometimes works for me (I am quite sensitive to low frequencies and I’ve had a few hums to deal with over the years) is to tell myself that there is nothing to worry about, the hum is not a problem, and gently direct my attention elsewhere. Or imagine you have a big volume control like on a hifi, and you are turning down the volume of the hum with it. Human hearing is amazingly malleable – people can become very sensitized to certain sounds, but equally they can become desensitized to sounds too. So the trick is figuring out how to take a bit of control of that process.

    I hope this helps somehow.

  8. That’s exactly what I’m hearing right now and it is 2:00 am , so annoying ? I’m in Maryland . Hope it’s construction sounds like I read on a comment above. I don’t want to get all anxious and paranoid.

  9. Does it sound like a set of 4 pules with a 2 second gap at the end, repeated?

    I’m in the Tyne Dock area of Newcastle and it’s pretty loud here at 2:42am, I’m new in the area so unsure if this is a regular thing.

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