Hi Mazda forum! I'm new here and a week-old owner of a 2015 Mazda 3 sedan. Love the car! But there's one noise that's making me slightly worried. Below is a shameless copy-paste of a topic I created on the Mazda subreddit.
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Since last week I am the owner of a Mazda 3 sedan from 2015 with the 2.0L NA engine and manual 6-speed gearbox. It's done 91.000km. When I go onto the highway and I drive around 105km/h I hear a droning noise. It's in the low frequencies (~170Hz) and it pulses rhythmically. Changing speed does not make the pulsing quicker or slower and when I drive below 95km/h or above 110km/h, the noise is gone. I can hear it in both 5th (~2800RPM) and 6th gear (~2100RPM) and steering has no influence on the sound.

I've made recordings with a fieldrecorder (Olympus LS10) because iPhones do not seem to pick up the noise. I'll share two versions of the recording. The original of course, but also one with some EQing to make it more noticeable. A low shelf (52Hz), high shelf (409Hz) and a +12dB boost at 170Hz. Please listen to these with headphones as the noise in question is hard to hear on small/tinny speakers.

My current hunch is that the noise is amplified or even caused by resonance. The actual source of the noise is unclear to me. It could be wind noise that starts creating a tone at certain speeds (think of panel gaps, the way a flute works) or it could be a rotational(?) noise amplified in the cabin.

I don't think it has anything to do with tyres. It has Bridgestone tyres (215/45R18 - Left 5.9mm, Right 7.5mm) at the front and Pirelli's (brand new) at the rear.

Frequency spectrum with the noise highlighted.

I've found these other threads/comments with the same description - although this all seems to be the 4th gen M3:

• Thread
• Comment

Curious to what you all think. I hope it forms no risk/danger to the mechanical state of the car!

 

Welcome to the forum

 

Thank you!

 

This is a great video with the sound frequency graph. I don't need to hear the noise(looking at the sound graph) to suggest that you take it to a service shop that specializes in chassis suspension service alignments, and sells tires.
That sound and looking at the graph may be a tire that is starting to separate internally? Or it may be drivetrain related. In either case these are GUESSES on my part and no one can analyze the exact problem without physically looking at and test driving likely lifting it up on the lift preferably a 2 post lift so the you can start the engine and place in drive and run the transmission in drive.

 

I am going to a Mazda dealer to have it checkout out come Tuesday (I’m going there anyway to have Apple Carplay installed). I asked about it over the phone and they suggested to test drive it.

I’ll see what that brings!

 

I took it to the dealer and it turned out my left wheel bearing was broken. I had it replaced and it did remove a noise I heard above 50km/h. However, it did not remove the noise that I posted about and that I demonstrate in the video. That leads me to think that the 105km/h noise, is most likely caused by turbulence resonating with exterior gaps or e.g. mirrors.

I might try to drive with the mirrors folded in (of course only on a straight, empty bit of road).