Need help diagnosing a rattling sound. Mazda Dealership thought it was tensioner assembly and replaced it but the sound has persisted. I also recently changed idler pulley so it's unlikely to be that.

2011 Mazda CX-7 2.5L Automatic with ~46k Miles

Video Link:
Video Link:

 

Welcome to the forum.


Sorry I listened at least twice each video, with all the surrounding other noises I can't hear what you are hearing with those videos?

Givin the year my first thought simply listening to your commentary would be something in the exhaust system is needing to be looked at as you mention it seems to happen on cold starts. And it does not help that you keep changing the RPM in the second video up and down...... Otherwise you really need to find a quiet place with less background noise and retake and repost your videos?

 

Hey Callisto, thanks for checking out my videos. I thought it was pretty obvious in the second video, particularly as soon as I start moving. Did you try listening to it with headphones?

But I agree with your initial suspicion, probably something having to do with the exhaust system, since it's for sure not coming from the serpentine belt, pulleys, accesories etc.

 

@Callisto So I am starting to think it is either the catalytic converter or catalytic converter heat shields since the noise is coming from the front underside of the car.

I don't notice any driving issues (loss of power, low mpg, white smoke, etc.), no check engine lights, and I assume the dealership didn't find any codes.

Is it possible for a catalytic converter to start rattling without causing any of the above problems? If not, then I am left with the conclusion that it must be a loose heat shield.

 

Yes the shield could vibrate or rattle when cold but the CAT still in working order. It may be as simple as pushing or pulling on the shield to slightly alter or reposition it to stop it from making the noise. When cold all you would be to do to test is with the soft part of your hand just tap on it to see if the sound can be recreated. You can also check other exhaust system parts as well.