Hi Rx-8 Club,

New owner here of a 192 Nemesis model Rx-8 44k miles - Just putting the car through the works and getting it to the best possible form it can be, absolutely love it, best drive I've had yet!

Was hoping to get your thoughts on a weird issue at the moment. When my car idles, I sometimes hear this rattle sound coming from underneath near the mid to rear section, please see the attached video for a sample. In the video the camera is pointing directly at the area where the sound is emitted from, right at the end of the decat - I was wondering if anyone has heard something similar or been able to isolate the issue to a specific part or symptom?

Please see post comments for video pointing to location of source.

I have checked the following things;
- Pressing the clutch does not stop or change the sound
- Pressing the gas for a moment get's it to stop until the RPM drops again.
- Sound is intermittent, does not always happen, but comes and goes when at low RPM.
- I have checked the heat shield underneath the muffler and the de-cat... Does not budge or rattle, both seem secure still.
- I can see that my engine mounts look a bit worn out and have not been replaced since 2006... going to replace these next month when I take it for a service.
- Sound is not coming from the engine at all and only happens at idle when the RPM drop below 1000.

Things I am checking tomorrow;
- Bolts around the de-cat and exhaust muffler are secure
- Heat Shield around the transmition.
- Anything else I can find online in time.

Many thanks and appreciation for your time in reading this and I look forward to hearing what you guys think.
Cheers

 

Here is a clip of where I have isoltated the sound to, it's a strange one lads! Any help is much appreciated

 

Any modifications done like an aftermarket exhaust or smt ..?
Maybe a small bracket or smt is loose. combines with the worn engine mounts you mentioned the vibration myt only occur during low rpms n will go away when the rpms r higher hence a lesser vibration transmitted through the car.
Since the mounts are already a thing to be replaced get them done n while the car is up on a lift properly inspect if anythng is loose under,

My 08- had a similar sound that jus occurs on low rpms jus as yours and of all things it was a vaccum leak due to a split air intake hose and yes the sound smhow came out frm undernear thr car around the tranny ..
So i suggest taking a thorough look at everything if u experience no power loss or stalling or gear grinding or tranny issues nothing much to worry about.

i watched the vid again n it does sound like a exhaust bracket is loose n poped out n hitting metal or like a heat shield

 

Thanks for the info mate! No after market stuff just yet - Car is pretty much stock other than the BHR Midpipe - It does drive / sound great and definately still nippy! Gearbox / clutch is nice and smooth too.

Had a good look today and checked a few more bits and pieces, heat shields seem okay which is strange, also gave the air intake host a once over and can't see anything just yet - I could see one of the hangars at the back of the midpipe is not fully in the rubber mount so gave this a go. Pending further testing on this.

I'll certainly give the entire underside a once over when the car is on the lift, mounts are definately needing a replacement, the left one is particularly low from other reference images. Looking forward to getting this one sorted as I love this car so much dude! Nice and calm at low RPM (other than the occasional rattle) then absolutely howls at you when you send it to 8.5k! Grips tighter than a nun too round a bend! (when it's dry).

Looking forward to the journey this car sends me on - Got some fun ideas I want to do (porting, turbo etc.), at least while petrol and rotaries are still around!

Cheers.

 

Hi All,

Quick update - I have found the cause of the rattle! It's the connection from my decat to the muffler - One of the exhaust bolts is done up super tight and does not have a spring so that the metal is contacting flat on this side of the gasket (I believe this to be the source of the squeeking and rattling) but on the other side, the bolt is on a spring and looks to be adjusted to a set torque.

Sadly the bolt on the spring has rusted a lot and I cannot seem to undo it, tried tightening and loosening, sprayed with WD40 and going to let it sit over night. Took a video of the difference in the gap on each side where the vibration must be causing this to rattle a fair bit. When trying to tighten and loosen the bolt I can hear the squeek sound that turns into the rattle from the low RPM. Atleast its not something mental! Phew.

So my question is - Are both sides of this connection meant to be on spring bolts? Or is it best to just have these as regular bolts? Also any tips for getting this rusty bolt sent to the abyss? Many thanks in advance my dudes!

All the best!
SliferGDL