# Why do cars do a similar sound on reverse? **URL:** \ **Category:** Factual Questions\ **Created:** [April 14, 2014, 9:57pm UTC](https://boards.straightdope.com/t/why-do-cars-do-a-similar-sound-on-reverse/686114 "2014-04-14T21:57:28Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Artemis\_Tardis](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@Artemis\_Tardis](https://boards.straightdope.com/u/Artemis_Tardis)\ **Post date:** [April 14, 2014, 9:57pm UTC](https://boards.straightdope.com/t/why-do-cars-do-a-similar-sound-on-reverse/686114/1 "2014-04-14T21:57:28Z")
It seems that many cars (at least here in Brazil, where we have petrol engines that range between 1.0 and 2.0) have a high-pitched hissing sound when on reverse. I noticed that on many different models, from a Honda Fit with a CVT gear box to an old Volkswagen GOL with a manual gear box. Does the engine work on a different way when on reverse? I always thought that the “reversing” happened on the gear box, with an extra gear… ---
**Author:** ![Superhal](https://avatars.discourse-cdn.com/v4/letter/s/b4bc9f/32.png) [@Superhal](https://boards.straightdope.com/u/Superhal)\ **Post date:** [April 14, 2014, 10:05pm UTC](https://boards.straightdope.com/t/why-do-cars-do-a-similar-sound-on-reverse/686114/2 "2014-04-14T22:05:39Z")
Have not noticed it at all. ---
**Author:** ![Mr.Kobayashi](https://avatars.discourse-cdn.com/v4/letter/m/4af34b/32.png) [@Mr.Kobayashi](https://boards.straightdope.com/u/Mr.Kobayashi)\ **Post date:** [April 14, 2014, 10:09pm UTC](https://boards.straightdope.com/t/why-do-cars-do-a-similar-sound-on-reverse/686114/3 "2014-04-14T22:09:10Z")
Dunno about a hissing sound, I always hear more of a whirring, it’s due to a [spur gear](http://auto.howstuffworks.com/question522.htm) being used in reverse. ---
**Author:** ![Superhal](https://avatars.discourse-cdn.com/v4/letter/s/b4bc9f/32.png) [@Superhal](https://boards.straightdope.com/u/Superhal)\ **Post date:** [April 14, 2014, 10:12pm UTC](https://boards.straightdope.com/t/why-do-cars-do-a-similar-sound-on-reverse/686114/4 "2014-04-14T22:12:06Z")
Oh, thought of something. Are you certain it’s not coming from the steering? Power steering makes a high pitched sound when the wheel is turned and the car is stationary, such as backing out of a parking space. ---
**Author:** ![Artemis\_Tardis](https://avatars.discourse-cdn.com/v4/letter/a/4bbf92/32.png) [@Artemis\_Tardis](https://boards.straightdope.com/u/Artemis_Tardis)\ **Post date:** [April 14, 2014, 10:15pm UTC](https://boards.straightdope.com/t/why-do-cars-do-a-similar-sound-on-reverse/686114/5 "2014-04-14T22:15:44Z")
pretty sure it comes from somewhere between engine and wheels. The sound is more noticeable when reversing faster… ---
**Author:** ![Superhal](https://avatars.discourse-cdn.com/v4/letter/s/b4bc9f/32.png) [@Superhal](https://boards.straightdope.com/u/Superhal)\ **Post date:** [April 14, 2014, 10:18pm UTC](https://boards.straightdope.com/t/why-do-cars-do-a-similar-sound-on-reverse/686114/6 "2014-04-14T22:18:29Z")
> [@demian\_travis](#): > > pretty sure it comes from somewhere between engine and wheels. The sound is more noticeable when reversing faster… Most likely doppler effect then. > **[Doppler effect](https://en.wikipedia.org/wiki/Doppler_effect)** > > The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The Doppler effect is named after the physicist Christian Doppler, who described the phenomenon in 1842. A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, ident When the... ---
**Author:** ![Mr.Kobayashi](https://avatars.discourse-cdn.com/v4/letter/m/4af34b/32.png) [@Mr.Kobayashi](https://boards.straightdope.com/u/Mr.Kobayashi)\ **Post date:** [April 14, 2014, 10:19pm UTC](https://boards.straightdope.com/t/why-do-cars-do-a-similar-sound-on-reverse/686114/7 "2014-04-14T22:19:46Z")
> [@demian\_travis](#): > > pretty sure it comes from somewhere between engine and wheels. The sound is more noticeable when reversing faster… If it’s [this](http://www.youtube.com/watch?v=5kz1HD7sHNI&feature=related) kind of sound it’s the spur gears.