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2012 Mazda 3 Touring Hatchback: Rattling Noise Under Car

About a month ago, I started noticing a very loud, annoying rattling coming from under my car. It is very apparent over any imperfection on the road. At first I thought it was the sway bar bushings needing to be replaced b/c I know Mazda has had problems w/ that w/ these cars. Those were replaced last week and I was so excited to get back in it and not hear the embarrassingly loud noise but nope, didn’t fix it. I should have probably got under the car on a ramp first before assuming to be honest but that’s my mistake.

I have isolated the noise (or so I think) to this area of the car. The image is below. The circle was from a different attempt to show people the area in which the sound was coming from but I have since put my car on a ramp and I believe it’s coming from where the arrow is pointing. If I’m not mistaken, the bulging area that is circled in the spare tire housing compartment, right? There is a metal bracket (for lack of a better term) that is going down the compartment and then it connects where the arrow is pointing. Here is the image from the passenger side of the car:

The quality of my ride is not impacted at all by this nor does it seem like it’s compromising the safety which is important to me as I have a 35 mile highway commute.

In order to get a better understanding of the annoying rattling sound, I took a very sloppy video b/c I feel the sound might give more detail as to what the issue is. Keep in mind, I am lightly tapping on the compartment and if I were to hit it harder, the sound is much louder.

Here is that video:

I am hoping someone here can say “yes, I’ve had that problem in the past and this needs replaced”. Honestly, it sounds like a loose bracket but I’m not too much of a car person to say what it is and it isn’t. Hoping this forum can help me out.

If you have any ideas, please let me know as well as if more info is needed. It doesn’t seem like it’s impacting my ride quality at all but it is noisy and embarrassing.

Thanks in advance!!

Did you look inside the spare tire well for any thing loose or rolling around?

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Yes, that was the first place I looked when I determined the area that is problematic. I have a Weathertech liner on top of the standard liner so something getting down in there deserves a medal lol! Once I got back there, I started tapping around the sides of the compartment and there’s no noise, at all. All the noise seems to be coming from underneath the car. One test I did want to do but no one was around, was to get underneath it w/ the spare exposed and tap to see if the noise is heard from inside. I don’t believe that will lead me down any paths towards success but you never know. It is something to test regardless.

I appreciate the response!

The vid is really zoomed in, but it looks like you’re tapping on the fuel tank. As such, I’d first check that the straps are tight and the bolts holding the straps are similarly tight. If all that checked out, I’d be looking at the filler neck, the fuel lines, and the fuel pump for a loose fit.

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Unfortunately it wasn’t zoomed in but instead that’s as far away I could get it knowing I was pointing at the right object underneath lol. I only had very small ramps so my wiggle room underneath wasn’t ideal. This is why I included the first picture to show the compartment I was tapping on from a different, better angle. I appreciate the info, regardless, and will certainly keep this in mind next time I start to troubleshoot it.

Thank you very much!

EDIT: I just Googled fuel tank straps (again, I’m not the best w/ part names or cars in general hence why I’m here) and those do look like what I’m seeing underneath which kinda leads me to believe this is the fuel tank and not the spare tire compartment I had initially thought. Thanks again!

Sure. Oh, another thought. If you can get your hands on an inspection camera, it might be worth peeking above the fuel tank. If a rodent decided to store a food cache there, what you’re hearing could just be an acorn rattling around.

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This is good info as well, Shadowfax. I appreciate it! I don’t have that equipment but it doesn’t mean I can’t find someway to figure that out.

The more I research it, I am really looking at these fuel tank straps as the culprits. Prior to getting on this forum, I tried to research all the part on the underbody of cars and couldn’t find a damn thing. An hour here has proven to be more useful of half a day of researching on my own. Also found something that suggests caliper pins and how I can rule them out (although, based on my video, I don’t see how they’d be the culprit since I’m nowhere near the brakes when recreating the sound). Thanks again!

So new development (and I probably should’ve prefaced this).

I got rear brake work done a couple months ago and noticed this happening afterwards. I read another forum about calipers, like I mentioned above, and also another thread and someone getting pads installed backwards. I’ve dealt with calipers before and they caused a terrible grinding sound which I’m not hearing now. If there’s no bumps, everything seems perfect. I just said “screw it, let’s rule the brakes out tonight”. Just got done driving around and drove over an area where I heard a great deal of noise, circled around and went over the same area except this time, applying a good amount of pressure on the brakes. Sure enough, when braking, I barely hear a thing, if anything at all.

Does this spark any thoughts in anyone’s head? I’m taking it to the shop first thing tomorrow and will let them keep it until they can get to it but I’d like to go in loaded with possibilities to give them bc this is driving me nuts lol. All I know is I drive 70 miles round trip on the highway for work and I’m not risking anything is brakes are a factor.

Again, thanks to everyone for looking and offering their suggestions.

Sorry if there’s any typos. I tend to miss them while using my phone

There may be some spring clips missing from the brake pads or caliper brackets. Without these spring clips the rattle noise can be a real nuisance.

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Thank you for the suggestion! I’ll make sure to suggest this. Appreciate it!

Ok, solution:

The rattling around my tank is still a mystery and we’ll deal with that later. My ride is now quiet and it’s bc the morons that put my brakes on put them on backwards. We’ll be having a conversation tomorrow but just in case anyone in the future reads this thread, please check that.

I appreciate everyone’s time and responses. My headache is finally gone lol