Hi guys, I desperately need your advice. I just noticed a strange sound in my new car a week after purchase. Any idea what could cause it? It's noticeable only while idling. Noise goes from the rear end, probably exhaust related.
I uploaded video on youtube
Please turn up the volume to hear that.

Update:
The Reddit user just shared the TSB about a similar issue. It seems like this is the case because my wife filled the tank for the first time after purchase that day and added more fuel after the first pump nozzle shut off
MC-10209728-0001.pdf
APPLICABLE MODEL(S)/VINS
2016-2022 CX-3
2013-2022 CX-5
2017-2018 Mazda3
DESCRIPTION
Some customers may complain about a tapping or knocking noise coming from the rear seat after fuel fill. The concern
will likely occur if the fuel tank is overfilled (more fuel is added after the fuel pump nozzle shuts off automatically) or filled
up normally in high ambient temperatures and the fuel expands.
No repair is needed. Explain to the customer not to continue filling after nozzle shut off. Refer customer to Owner’s
Manual Warning.

 

Sound and noises are hard to diagnose with videos, however you are still under WARRANTY and my string suggestion is to go to your local Mazda dealership ASAP and have the service writer physically listen to the noise.

That noise is not normal or common

 

Thank you for the reply! It's hard to reproduce this noise because it doesn't always pop up. I couldn’t reproduce it today, so all I have is just the footage. I will definitely show the video to the dealer. I just wanted to get a third-party opinion, maybe someone on the Mazdaforum has had a similar experience, so I won’t be fooled by the dealer telling me that the noise is normal

 

The noise in the video is not normal!!

However, because it appears to intermittent unless it is making the noise when you go to the dealer they will not likely do anything unless you are willing to leave the Mazda with them a day or so. And they will not likely offer a loaner because it is not a concerned service yet?

The good thing is your concern will be logged on your VIN record.

 

I must be deaf, I couldn't hear anything noticeable.

 

I have to agree with Grim.
While I have lost some of my upper frequency hearing my low range is fine and don't hear anything except exhaust note.

 

The sound I hear can best be described as a washing machine on spin cycle. LOL

 

Huh????

 

I honestly can't tell what that is. Unless there's something noticeable when standing outside of the car, I wouldn't worry about it.

 

I played the video over our sound system and asked everyone what they heard.

Answers.

a bubble in a tire
a bent wheel
a squirrel that was run over and the remains are now hitting the wheel well
mine ....a washing machine on spin cycle
My lot maintenance guy said "sounds like my car"