Hey mate
Thanks for the update. At this point I’m leaning towards one of the secondary cats (at least on mine).

 

No prob.

Could very well be. From everything I've read, it does not sound like anyone has investigated that part yet.
I'm not much of a gearhead, so I googled secondary cats to find out what and where they are. Being they are exposed and easily seen or accessed, is it safe to conclude the sound could be coming from the inside of one of the two widened pieces? Again, I pushed on and knocked everything, including that part and nothing seemed loose. Are there components inside the secondary cat pieces? Lastly, if they do discover it's from those, how is the exhaust system removed (cut?) and re-attached? I'm starting to wonder how the new connection could be made as good as how it came out of the factory and not separate over time.
Sorry for all the questions, I need to learn as much as I can about these components.
Thank you

 

No worries mate.

Inside of them cats usually have the catalyst honeycomb insulated with either metal mesh or fiber mat. In the case of Lexus/ Toyota I’m not sure which insulation material they use but in either case the rattle would occur when the honeycomb comes loose or gets damaged over time.
I noticed a difference of the sound when I was inspecting the exhaust. My passenger side cat gives a slight yet noticeably different sound when tapped with a mallet. I can see that would get amplified to a louder rattle at the correct frequency.

Inspection wise, there’s nothing much you can do. Could either drop the whole midpipe section and have a look with a borescope or cut a hole on the cats and see. As you can see in the first image (From an eBay listing) the cats are quite further down the exhaust pipe and there’s a slight bend before that. Hence a borescope would be the only way to see what’s going on. A decent exhaust shop should carry one.

Fixing wise at this point what we can do is:
1. Take both the cats out and get a custom midpipe section welded in.
2. Replace with an OEM mid pipe. With cats I can see the dealer would ask for a small fortune for one.
3. Go for an after market mid pipe replacement like Invidia, Tsudo etc. You could either go full catback (I’m talking about primary ones here) with mufflers or just a midpipe with OEM mufflers.

I’m leaning towards the third option and just getting a midpipe with hi-flow cats and keeping the OEM mufflers. I daily my car and wouldn’t like to deal with any kind of exhaust drone. I understand there’s the risk for a check engine light with an aftermarket exhaust system. If it comes to that will probably have to run some Oxygen sensor spacers with it to get rid of it.

I’m currently in the market for a good midpipe setup and considering all options. Will advise on the progress. Until then I just crank up the music a tad bit.

Image 1:

OEM midpipe section (EBay listing)

Image 2:

Aftermarket midpipe ( Invidia)

Cheers and thanks for reading

 

Fantastic info, thank you! Very clearly written and explained. I guess my last question would be is how/why does the sound only come when moving forward and not in Park?
Okay, keep us posted on what you end up doing and if it cures the sound!

 

alot of those "custom" are prone to droneing..if U have ever experienced it U dont want it ever again.

 

Different harmonics when the engine/drivetrain is operating at different speeds or under different loads. Most car rattling/buzzing is like that... only at certain points and not all of the time.

 

Man I’m commenting to follow up. My 2022 started doing it around 43,000 miles. I mentioned it to the dealer two times and they gave up searching. Of course, now I’m out of warranty cuz of time. I’ve been checking everything in the car and I find nothing. Unfortunately I don’t have a lift so my inspection on the underside is rather limited.

 

If you brought up the issue while under warranty, technically they owe you a fix even after it runs out.

This is turning into one of those rare mysteries that has yet to be solved. I'm going on three years of the noise with no luck yet. Whoever finds out the source is going to have to win an award!!!

 

Adding to the fix list, another bush mechanic fix exists if it indeed relates to a rattly cat.

You can give it a good whack and make a dent so that the dent itself will clamp the rattling part inside. (Or drill in some screws.)

Do this at your own risk since you are likely to end up damaging/ crumbling the catalyst inside even more and worsening the rattle.

Seen people in YouTube do this and have no idea about the longevity of this fix (hack job).

Cheers

 

What’s going on guys. I come with a positive update. I wrapped the questionable secondary cat with exhaust wrap and the noise is barely noticeable now.

Long story short, before pulling the trigger on a midpipe or custom exhaust work I wanted a test a theory I had. As the noise (at least in the case of mine) is quite intermittent and acts more like a resonance reaction for a specific frequency, I thought what if I change the natural frequency of the object; in my case one of the secondary cats. So I used some fiberglass exhaust wrap and some proper plumbing clamps (not the steel cable ties that come with the wrap kit) to secure the it, to wrap only just the secondary cat tightly.

Been testing the setup for a little while in varying driving conditions and it has held up nicely and most importantly the noise is pretty much non existent. During the last couple days I only heard the noise twice and I’d say it’s 90% quieter and lasted for less than half a second I’d say. Again you wouldn’t really notice it if you didn’t know that used to happen beforehand.

I know this is not a full on FIX for the issue and I would eventually be doing a custom catback exhaust setup down the line. But if anyone would like to test it out it would only take about $50-$60 and a couple hours of time. And I recommend you guys give it a go.

Cheers and keep us updated

 

Wow, thank you! That is huge news! So it was/is indeed the cats causing this noise! Great work by all who honed in on it. So I fully understand here, the physical piece of the secondary cat is moving and vibrating? Not something inside of it? And since there are two of these, is it just one and not both? (I only googled the term and see there are two of these secondary cat things....)
For those of us still under warranty, I wonder know how the dealer will address it when I tell them where it's coming from...

 

I spent a good hour with a mallet tapping the length of the exhaust and the only place where a suspicious sound was coming from was the passenger side secondary cat (Yes, there are two secondary cats after downstream O2 sensors). Bear in mind that the sound difference itself was really subtle and I doubt a routine inspection wouldn’t say it’s bad unless someone is specifically looking for the source of the issue. In my case the cat didn’t sound like it had loose debris in it, more like it rang in a different tone compared to the rest of the midpipe when tapped.

I don’t think the dealership would replace a part under warranty just because a customer asks them to, unless they themselves determine it’s faulty. You can try to talk to a service advisor and have a chat with a master tech, take them with you on a test drive to demonstrate the noise first. And point them to the direction of the rattly cats. So they know what to look for at least.

Wish you good luck