# Strange engine sound MX5 NBFL

**URL:** <https://community.cartalk.com/t/strange-engine-sound-mx5-nbfl/178801>\
**Category:** Maintenance/Repairs\
**Tags:** miata-mx-5, mazda\
**Created:** [August 18, 2021, 7:06pm UTC](https://community.cartalk.com/t/strange-engine-sound-mx5-nbfl/178801 "2021-08-18T19:06:46Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Rhadamenthos](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/rhadamenthos/32/24499_2.png) [@Rhadamenthos](https://community.cartalk.com/u/Rhadamenthos)\
**Post date:** [August 18, 2021, 7:06pm UTC](https://community.cartalk.com/t/strange-engine-sound-mx5-nbfl/178801/1 "2021-08-18T19:06:46Z")

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Hi there,  
I found out at a cold start that I had a strange ugly engine sound instead of the sweet purr it used to be. I made a video after a cold start, at idle : [Bruit étrange moteur - YouTube](https://youtu.be/DqG8TN9Tog4)

I’m a bit worried something bad happened to the engine. FYI, I changed the calorstat and the alternator + belt recently. But I don’t know if there’s a link.

Do you have any idea what’s going on ? Thanks a lot.

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**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\
**Post date:** [August 18, 2021, 7:34pm UTC](https://community.cartalk.com/t/strange-engine-sound-mx5-nbfl/178801/2 "2021-08-18T19:34:59Z")

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I listened to the video… exactly what noise are you referring to?

Since you changed the belt and alternator and… I don’t know what a calorstat is… this is a US site, we may have a different name for it, maybe the thermostat?? I’d suggest maybe you remove the belt, start the engine and listen for the same noise. If it is still there, it is a new problem. If it goes away, it is related to the belt and the new alternator. Possibly the pulley tensioner.

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**Author:** ![jtsanders](https://avatars.discourse-cdn.com/v4/letter/j/c2a13f/32.png) [@jtsanders](https://community.cartalk.com/u/jtsanders)\
**Post date:** [August 18, 2021, 8:22pm UTC](https://community.cartalk.com/t/strange-engine-sound-mx5-nbfl/178801/3 "2021-08-18T20:22:21Z")

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Yeah, calorstat is a thermostat.

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**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\
**Post date:** [August 18, 2021, 10:38pm UTC](https://community.cartalk.com/t/strange-engine-sound-mx5-nbfl/178801/4 "2021-08-18T22:38:41Z")

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Describe the conditions the sound occurs. Only during cranking? Only after cranking, at idle warm up?

Commonsense says to verify the affected belt tension and routing is correct.

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**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\
**Post date:** [August 19, 2021, 6:17am UTC](https://community.cartalk.com/t/strange-engine-sound-mx5-nbfl/178801/5 "2021-08-19T06:17:23Z")

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Different car, but terrible noise like valve clatter at startup, ended up being a belt tensioner.