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This is real life issue I am having currently and I am puzzled as to why it happened. I have lived over the subway lines (two actually each going in the opposite direction, two sets of tracks) for two years. The noise has always been a soft background hum, with an occasional louder train (that usually needs maintenance), hardly noticeable. One early morning near the end of January I was jolted out of bed by a loud noise. Turns out it is the subway. It is as if someone turned the volume up from 3 to 8 all of a sudden. Noise much louder (both tracks), last longer and there is shaking indoors too. Some small variances in the loudness of each train, but all much louder. The quietest train now is much loudest then the loudest one was before. I know that no changes were made to the tracks, trains, schedules or my building. What else could have caused it - noise from subway became much louder overnight?

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closed as too broad by Fred, user259412, Wasabi, user16 Apr 21 '18 at 18:34

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Why not state the city, subway operator and track section? $\endgroup$ – Transistor Apr 20 '18 at 23:52
  • $\begingroup$ How would that help? $\endgroup$ – Vaness Apr 21 '18 at 0:04
  • $\begingroup$ Because someone who knows the subway might have some knowledge of engineering changes that have recently taken place, of course! $\endgroup$ – Transistor Apr 21 '18 at 0:09
  • $\begingroup$ No changes - have been talking to a relevant person within the transit authority (who even visited), have had an inspection done of the tracks underneath (twice). No changes what so ever. And again, it happened over night. One Friday night I fell asleep to be woken up by the noise at 6.30. Unlikely major changes happened Friday night....But if it helps thee city is Toronto, Toronto subway $\endgroup$ – Vaness Apr 21 '18 at 0:16
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It is possible that because of percolation, the moisture content of the layer of dirt between you and subway has changed to near optimal compaction, which is in the range of 12 to 24 % in siltyclay, assuming your strata is CL, ML, SC. These are sensitive to moisture ratio and at optimal compaction transmit sound better.

Some change in moisture is seasonal, therefor it could go back to initial condition. But if a main sewer or water line has cracked, there is room for concern.

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  • $\begingroup$ Not sure what type the soil is below. You think the moisture level could stay the same over a period of 2 1/2 months? $\endgroup$ – Vaness Apr 22 '18 at 2:10
  • $\begingroup$ Sorry that was meant to say Do you think.... $\endgroup$ – Vaness Apr 22 '18 at 13:03
  • $\begingroup$ The only way to arrive at a meaningful estimate is to test. There are fast tests, such as a calcium carbide reagent type. Regardless of method one needs to have the help of a geotechnical engineer or at least a lab and an hourly technician. Your local building department may have useful information and public domain searchable geology reports. $\endgroup$ – kamran Apr 23 '18 at 3:21
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If you were to stand next to a long train going by at speed, you would likely notice that some cars are incredibly noisy while others are relatively quiet. the most likely answer to your question is that the railroad cars now in service on that portion of track are different from those previously used.

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  • $\begingroup$ Appreciate the answer but no. Subway train fleet running on full capacity no exchanges or new trains or cars planned until 2020 - info from the transit authority and their wiki page. . When it does happen it will be with pomp and politicians like it was on another line they did recently and not overnight and without telling the public.. Occassionally a train is removed for wheel maitenance overnight and returned in a day or two $\endgroup$ – Vaness Apr 20 '18 at 22:02
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    $\begingroup$ Wow! the main source of noise is in the wheels and rail surfaces. I wonder what happened! $\endgroup$ – niels nielsen Apr 20 '18 at 23:00
  • $\begingroup$ Could the 'path' of the sound between me and the train have changed significantly (i.e. the ground between) in which case is the building unstable,.. $\endgroup$ – Vaness Apr 21 '18 at 0:03
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    $\begingroup$ if the ground froze between the tracks and your house, it would make the noise much, much worse! $\endgroup$ – niels nielsen Apr 21 '18 at 0:37
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    $\begingroup$ Well the frozen ground possibility is one reason that stating your location was helpful. That wouldn't have been a problem in Athens, for example. $\endgroup$ – Transistor Apr 22 '18 at 9:00

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