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..

46 Replies to “Mysterious night-time pulsing sound”

  1. I live in Melbourne, Australia, and I have been woken at 4am each night for the last 4 nights to a low-frequency pulsing sound. On the third night my whole bed was vibrating, and it was impossible to go back to sleep until it stopped. It has always stopped at around 10am, but today I sit here writing this at 1pm and it is still there, slightly less noticeable (probably because of the noises in the environment now that it’s Saturday afternoon). At first I wondered if my downstairs neighbour was using a CPAP machine or something similar, but I listened near her door and couldn’t hear anything. Perhaps I’ll listen at her bedroom window if it happens tonight. I always wear earplugs when I sleep, and curiously, the pulsating noise is actually more noticeable with earplugs than without. Perhaps it’s an auditory hallucination? Last night I was able to get back to sleep by playing white noise through in-ear headphones – but I would really rather this not become a new routine. Today I plan to do further research into the source of the sound.

  2. I’ve heard low frequency regular pulsing that comes and goes (almost all the time) for a few years. We moved half a mile to a different house just over 4 years ago and this is when I started to hear it. At first I put it down to my ears and some kind of inner heartbeat or something as it always happened at night. But 4 years on, as I sit here with my family around me, I am still hearing it come and go (and so can my husband). We live near a railway, a scrap metal yard, sewage treatment works and about a mile out of the town centre. We also live near a solar farm and 5 miles from a government underground city in Corsham. We live in Melksham Wiltshire. This is the most prominently I’ve ever heard it and we are in the middle of the COVID-19 breakout. (2020)

  3. I live in Leith. I hear a low pulse/vibrating. It’s like the low frequency him from a car engine that’s stopped outside a house. I figured out one night that it is coming from ships docked at Ocean Terminal/Forth ports. It’s horrible.

  4. I was once pulling an all nighter, until around 3-4am I start hearing this pulsating noise. It sounded like it was coming from my living room but I can’t tell for sure, since I didn’t want to investigate and find god knows what. It lasted approximately 3 minutes and was ranging from higher to lower pitches, mostly pulsing towards the louder and somewhat lower tone. I’m not sure what it could’ve been, although I will say it resembled the sound that a generator In a movie would. As in thy kind that’s used to “take over the world.”

  5. We heard similar in Alaska – sounded like deep base electricity waves pulsating across the sky. Eerie sounding- we couldn’t figure out what it was.

  6. Second yeah of hearing this. Missouri, USA.

    Last year real close, loud. To the South of me.

    This yeah, faint, far, and to my easy. Will try to record soon.

  7. My husband and I heard a stranger pulsing sound the last two nights. The sound was repeated about a minute apart and went on for quite some time.
    I tried listening to your video to see if it was the same, but it appears to have been taken down.

  8. I experience a pulsing sound in my right ear only.
    It becomes a apperent when a kettle approaches boiling point.
    The pulsing sound is caused by my ability to hear higher frequency improves in sync with my pulse.
    The pulsing stops when the ambiance noise ceases or I stick my finger in my right ear. The higher frequency sound becomes louder if I tense the musculsame in my neck.
    It does not happen with all sounds.
    Driving a car sounds like sound reflecting back off of lamposts.

    Another night time low frequency sound I traced to my mains driven Soni radio alarm clock. Moving it off the hard suface of my bed side cabin ate was enough to silence it. The low frequency hum. (50 hz x 2) being low did not seem to Come from any direction.

  9. Heard this extremely faint deep low frequency pulse, most definitely not my heart beat. It was rhythmic and between 1130pm to 1am onwards till I was able to sleep. No dripping distance taps or ticking clocks. No local road or engineering works. I live near M25 junction 7.

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