Mystery Chatter/Rattle
 

Hey guys Ive been chasing this chatter for about a month now, Ive been searching on here getting new ideas but everything I try ends no where.

The chatter seems to be load related vs rpm related as it only really occurs from 7-9k+ rmp at WOT. The sound does not happen if I creep up to red line. The noise is present in 2nd, 3rd and 4th gear (havent tried 5th or 6th --It does not appear to occur in 1st gear or at least its not loud enough)

I'm not experiencing any powerloss or any unusual CELs.


So a little back story on how I got to where I am...

It all started with this insane vibration I developed and felt in the cabin. For a long time I attributed it to poly bushing in the diff carrier mount. Then The chatter developed or at least became much much more apparent ( I vaguely remember hearing it months and months ago while red lining beside a concrete barrier, but It was not a regular occurrence).

So I start chasing the possible source of the chatter and find that one of the two lower of the bolts on the passenger side engine cradle mount was gone and the other lower bolt had worked its way loose. The top nut holding the cradle in was also loose.

I get a replacement bolt and tighten everything up and immediately notice that the excessive vibration is gone and the chatter has also disappeared.... Until the next day...

The chatter returned and the real search began.

I checked:

• Heat shields around the exhaust
• motor mounts (urathane filled) Both sides
• engine cradle mounts -both sides
• Alternator bolts
• starter bolts
• ac compressor

Please find my mod list in my sig.



Im having a hard time capturing the noise as the sound of my exhaust/wind noise kills the sound quality.


Any Ideas or suggestions are welcome... Thanks

Does it happen when the engine is cold? I know its not wise to redline before your at operating temperature (~10 minutes) but I was having a similar issue to you and after chasing my tail for around 6 months I noticed the noise would only happen after I drove for a while. I tried instilling the heater core orifice adapter, propylene glycol coolant, the mazmart water pump but nothing worked. The sound would always come back, around the time the thermostat was open, but the noise and a closed thermostat were not mutually exclusive. I got new BHR ignition coils, plugs and wires, and still nothing. My car has 105,000 miles on the original engine (still good compression!) and after physically listing everything I'd done I realized the only thing I hadn't considered was my fuel system. Because of a recent run in with inversed polarity I knew my fuel pump was functioning, but my car was still on original injectors and probably had never had the fuel system cleaned out. Last week I poured a bottle of gumout in my gas tank and so far I can't replicate the rattle. I'm not sure why the fuel system would result in this noise, but whenever your pumping a fluid through tubes it creates friction and heat and I figure if their was a bottleneck somewhere in the system it could easily be exacerbated by high heat. I believe the noise occurred in every gear, but wasn't noticeable in 1st because the high gear ratio makes you gain/lose rpm too fast for it to be noticeable.

Context: I have all the same mods but with BHR motor mounts and an OEM CAT and AEM intake

Interesting, now that you mention it it does seem to be less apparent when cold and much louder when hot... Ill try a bottle of gumout too and Ill post the results...

Thanks

Update:

I tried the gum out this past Sunday on half a tank of gas, and since then I have not been able to replicate the noise.


Thanks for the heads up Panda. Hopefully what ever it was is cleared up now. Still puzzles me exactly what is causing it though.

Are you sure you aren't running lean due to some inefficiency in the fuel system, and the noise you hear is actually knocking/detonation?

It does sound like it may have been detonation. I'd expect that to happen at lower than 7k rpm though.

OP, I am curious whether the rattle returns once you refill without the Gumout?

If it was knocking/detonation I would think there would be power loss... Idk Ive never really heard detonation on a renny.

If it is a deficiency in the fuel system im doubting its my fuel pump as it is fairly new so possibly injectors?

Im very curious as well...

I refiled after using gumout 2 tanks ago and the noise still hasn't come back.

Finished out the tank with the gum out and filled it with 93 and the sound slowly came back before consuming a 1/4 of the tank... But it is much quieter than before the gum out.

ok, I just got my third tank and the noise is coming back less violently as well. I burned that tank and am just refiled with some more gum out and am waiting to see whats up. I feel like if gumout made a change then it has to be fuel system related.... maybe the fuel pump has issues on a low tank? maybe clogged injectors? Im considering swapping to a 2nd get fuel pump but idk if thats going to change anything.

Well upon recommendation of a friend I tried swapping knock sensors with no luck. My fuel pump is only about 6 months old and after doing research failing injectors/clogged do not seem like a common problem with our cars. Not to say that its impossible but Im kind of at a dead end.

How many miles are on your car? Do you have a habit of running your tank down to empty? After 100k miles, two of my injectors were flowing 95% of rated flow rate, with dripping/poor spray patterns. FWIW, getting those cleaned seemed to help a little bit, but did not solve my problem.

I take it you sent your injectors away to get professionally serviced?

I have 160k on the injectors, and yea I have a habit of running low.

How many miles on your fuel pump?

100k miles on my fuel pump.
I had a local rotary shop pull the injectors and send them out. I also had the fuel filter changed (I have a series II). It was pretty gunked up. Unfortunately on the Series I, the fuel filter is not replaceable and you have to replace the whole pump.

Did you fix the problem? I'm having a similar issue. except mines happening around 3000rpm onwards. it's a slight metallic rattle. you can barely hear it

My problem has not been fixed. I suspect I have a more serious issue than clogged fuel injectors/fuel filter...

Did a fuel system cleaner make any difference for you? Im curious as to if we have the same issue. I just burned my second tank with gum out and after refueling the noise mysteriously retuned. I have an s1 with 105k on original injectors and fuel pump, so Im going to replace my pump and see if that makes a difference

I've had this problem since I got my rx8 ive been searching around for almost a year, I get slight hesitationin the higher rpms and a rattle/chattering at wot anywhere from 5500-8k inconsistently, its the worse and loudest at 7-8k , my car doesnt have the torque the other 2 rx8 have but runs and starts fine, I replaced coils, plugs , wires cleaned maf and ecc reset it all, no signs of low compression. Ive been thinking might be my fuel pump or filter

Mine just started making the noise yesterday. Most noticeable in 2nd and 3rd gear and above 3-4K. Sounds like predetonation, but hard to know. I actually feel a popping feeling in the shifter. I replaced my 2004 engine at 148K with a used 2005 engine with 40K. I've put 30K more on that replacement engine with little or no other engine problems. Since this is the start of spring, could it be a different mix of gas? i just filled up the day before. One thing I thought about was the ports that open at 4K and above.. I believe they are vaccum controlled and rotate.. wonder if something is up with that... UGH.. why can't this car just be reliable.. I work on it almost as much as the Fiat I used to own!