Mechanic says first time he has seen such an issue in 30 years

[mazospeed]

So while driving the car, I started hearing splashing noises.

Took it to the mechanic, after looking at every thing he suggested that some thing could be IN the fuel tank. He removed it and found that the inner wall within the fuel tank is broken. Like it has been unattached some how from one end. Apparently these inner porous walls help make fuel less volatile by stopping and reducing its splashing inside the thank.

We got it replaced.

Now after hardly a few months, the SAME THING HAPPENED again with the new fuel tank and am again hearing the same splashing noises.

It is so rare that I cannot find anything on google and the mechanic said the first time that never has he seen or heard about any such issue in his 30 years of work life.

Any theories what is going on here. It is Mazda3 2008 SP25 (Australia).

 

[youri]

Could be a clogged drain where water is accumulating. Either the AC drain hose or the sunroof drain maybe ?

Seems like a few things could to lead splashing noises in cars in general: I Can Hear Water Sloshing In My Car - Why? - Car Super Care

If the sloshing sound came back after a few months of having the gas tank replaced, then it is likely the gas tank wasn't the cause (it may still have needed to be replaced, but may have not been the source of the noise).

 

[Havokk]

Get a buddy and have them try to pinpoint where the sound is coming from as you accelerate, make turns and use the brakes. Its a win, win. As you might find where it's coming from, but also have a great laugh as your buddy tries to locate the sound!

 

[mazospeed]

Apparently it is baffles becoming loose and it is super common for Mazda3 of this generation.