05 Rx8 6mt 32,000miles RHD version. Completely stock. Same as UK-spec rx8.

It got very hot yesterday (Ambient 38degC approx 100degF) and I noticed that while accelerating, there would be a "resonating" sound that will appear between 2000-3000rpm in all gears and with or without a/c on. It sounds like a small coin sitting and vibrating against another metallic surface. Does not appear while revving in neutral or when decelerating across those rpms. At night when it is colder, it is less obvious. Some times it can be heard continuously while just cruising between 2000-3000rpm and while moving off from a standstill. Bearing in mind that mine's RHD (like the UK/Japan version), I hear it coming from under the centre console area but slightly off centre to the left. What could it be? My first thoughts would be transmission/engine mounts/ exhaust/heat shield.

Recent History: The day before the sound began, I had the front brake rotors skimmed, spark plugs + wires changed, and aircon refrigerant topped up. Ignition coils change 2 months ago.

Its not the "marbles in a can" sound of a bad cat but more of a faint resonating/vibrating noise that you would sometimes hear and feel when you are dragging in too high a gear at too low an rpm that the engine is about to stall. I seem to think its heat related because it started while the ambient was really hot. Another thing: I have a habit of REPEATEDLY accelerating and then shifting to neutral to coast and then when it slows down, I will shift back into gear and accelerate again. I do this on freeways to get better mileage but I don't know if I'm harming the gear box and syncros by doing this. So far, the gear box feels alright apart from some grinding/vibration at the instant when I try to engage 1st while the car is not stationary so I always try to avoid forcing it into 1st unless I have come to a stop.

 

1) You are probably hurting your gas mileage by doing what you are doing. The time spent coasting along is heavily outweighed by the amount of gas you are using to accelerate back up to speed.

2) Are you just feeling some firmness/stiffness getting it into gear or is it actually grinding? With all of your clutch play on the highway you might be in need of a new clutch.

3) Check the heat shield around your cat.

 

What gas are you useing ....reg-87oct or prem-91oct or higher?

 

Latest Update: Today, the resonating sound has gotten worse. It is no longer faint and no longer restricted to the 2000-3000rpm range. It also sounds like it is coming from the area between the centre console and the radio. While moving off in 1st gear, it will be heard from as low as idle all the way to 4000rpm. Thereafter, in 2nd to 6th gear, its will be heard between 2000-4000rpm. Previously, it did not happen while revving in neutral. Today, while revving in neutral, I hear it as the revs pass 3000rpm. If it is getting worse over night, I can only think that it must be the catalyser's inerts that are disintegrating and getting stuck in the pipe. It is beginning to resemble the characteristic "marbles in a can" cat noise that is discussed so much in this forum which is why I am thinking it could be the car.

Or it could be the tranny and I'm hoping its not. I ruled out the heat shield since that will not be something that worsens over a day.

Your views please...

 

Hi devil, I was averaging about 13mpg just driving normally while in gear. My "free gear" coasting has got me up to 16.8mpg. What I do is to accelarate to about 10mph above the legal speed limit and then shift to neutral and let it cruise down to 5mph below the limit and then repeating this. Of course I do this only when there are no cars in front or behind me. If this habit is hurting my gearbox, I will stop doing it. Gearboxes and clutches cost more than fuel

As for the issue of getting it into gear. It only happens while trying to engage first while the car is not at a complete stop (eg. 5mph). Its has that usual resistance that is telling me "you're still moving, don't force me into first" but if I hold it at that point of resistance without forcing it in, I feel some vibration in the gear ****. Its a vibration that feels like 2 parts rotating against each other. Synchros?

Will have the car hoisted to check the heat shield on Tuesday.

 

My last tank was 95octane. Today, I refilled with 98.

 

If I can cruise at a solid 80mph and get 28mpg highway and can average 20mpg consistantly with city and highway driving there is something else going on hurting your gas mileage.

The grinding you are feeling would be unwanted but expected.

 

Your deduction methods are flawed.

Get down and dirty, jack her up and check the shield.

It it's loose are torn it can change at any moment in time.

 

Hey you guys, thanks for your patience. Here's the latest update. Car was making that vibrating/resonating sound in all gears during acceleration between 2000-4000rpm. It has gotten louder. It sounds louder when hot and when cold, can hardly hear it. Now, can even be heard when revving in neutral when the revs are on the way up. No sound when revs are on the way down. It is most noticeble when the car is "dragging" itself eg. going up an incline/ramp at 2000-4000rpm. Sound appears to be coming from behind the radio, slightly off centre to the left.

Thinking that its a bad cat or heatshield, car was hoisted today. Lower insulator of exhaust manifold was loose towards the rear bolt (ie the bolt nearer to cat). While tightening, bolt broken. Drilled out, tapped and retightened with a new bolt. All other heat shields were secured with no "looseness". Cat was removed to check for broken pieces of ceramic. I was surprised to find that all the material inside the cat was completely removed and it was a straight through. Looking inside header, cat and midpipe, I found all to be very clean... no carbon, no catalyser fragments. One observation: front O2 sensor in the exhaust manifold was was almost completely white. Cat reinstalled. All rubber mounts related to the exhaust inspected and found ok. Engine mounts appeared good visually. After all that, the irritating noise still persists.

Removed glove box (mine is on the left as it is a RHD car), checked the area behind where the cabin filter and wiring harnesses are. Nothing unusual. Any more ideas?

 

A gutted cat will have a drone in that range under load.

 

Was there ever any solution found to this problem? My car just started doing it today.... between 2000-3000 it sounds like metal on metal vibrating only while accelerating and not while reving it in neutral.

 

Please give us some more info...model,year,miles,etc... What service and parts has the car had?. How many miles on plugs,coils,wires? What other mods have you got?...How long have you had it?... Have you ever done a de-carbon cleaner?

 

2005, Touring, 32,000 Miles. All recalls and flashes are up to date. Just changed the oil 1000 miles ago. Still original coils, plugs and wires....Have new plugs just had not put them in yet. I have an oil catch can...everything else is stock. I'm the original owner I purchased it in 2007 with 300 miles on it. I have never done a de-carbon cleaner. Thanks for response, any other info?

 

^OEM coils are only good for ~30k miles

 

Sounds like you are running lean

 

Would the bad coils cause a sound like this though?

I know the coils had a short life as did the spark plugs (thus why I already have a set ready to go. I'm an avid reader not really much of a poster. Also why i knew to search out this thread rather then start my own to avoid being flamed)

But I thought bad coils only caused a lack of power not a rattling sound at specific rpms.

 

This is one of those situations where it would be easier if we had the car in front of us. If you have any forum members near you, invite them over/ meet them to get their opinion. As for now, take a video (with the best sound you can; cause that is what you are saying is the issue, so we really need to be able to hear it in clarity). Also, take a pick of the inside of your CAT so we can see it to verify that it is not the CAT. An alternative is also putting on a midpipe (if you have one at your disposal). If the car runs fine on the midpipe, then it helps to narrow down the issue

 

I actually have some awesome local forum members so I will do just that.

 

cool, I hope you all are figure it out

 

Josh - I'll be headed to Canton possibly on Monday to look at a car...I can buzz by. Did it start when you pulled your wheels off though?

 

Just came across this thread. Mazda has a TSB that has to do with noise generated by contact between the wheel and the hub; has been common in new wheel installs or when painting rotors and hubs. Basically, the metal deforms and the releases causing a popping sound, very much like you describe. The cure is to remove the wheels, remove all paint/dust/crud from the surfaces where the wheel contacts the hub (both surfaces), clean them with a high flash point cleaner, then increase the torque on the lug nuts, 108 In-lbs I believe, someone correct me if I'm wrong on that. The fact that it popped up after service having the wheels off leads me to believe this may be the problem. It happens on my car occasionally if its been sitting a long time and I'll get a pop or two out of the wheels when I start moving.

 

Sorry, I haven't been on the forum for a while. Here's the update for the noise issue...Its actually a simple and embarrassing cause even though for weeks, it baffled all the mechanics who tried finding the source of the noise in my car. It turned up to be the little plastic one-way check valve along the vacuum hose that runs under the resonator. Its the same vaccum hose that connects the upper intake extension manifold to the vacuum chamber that controls the VFAD. Mine was tampered with and has an extra long rubber hose so at the point where it goes under the resonator, it actually became wedged between the ignition leads and a metal plate. At certain rpms during acceleration, it would resonate and make that noise. I only found out about it when I removed the airbox. All I had to do was cut the hose so it did not hang so low and the noise went away.

I hope this helps guys.

 

Josh fixed himself yesterday too. His metal catch can was vibrating against something else under the hood.

 

It's interesting that we both had problems that weren't really the car. But instead due to us tampering Strange that both problems appeared at the same range of rpms. Glad your car got fixed too.

 

Hi All,

I'm new to the forum and this will probably be my only post sadly, because i am selling my RX8. i really dont want to but thats life.

anyways in the searching and listening to all my cars noises i found i was having this problem as well, exactly as described by crave4speed

I found that my heat shield around the lower o2 sensor was loose and resonating badly.

ALSO the more interesting one i thought was the muffler, the muffler is welded to a set of brackets, on those brackets were two clips (looked like positioning clips for initial welding during assembly of the car) these clips were also vibrating, I stuffed a piece of fiber glass in between the muff and the clip and the sound went away. anyways, enjoy your RX8's everyone i know i will miss mine very much! hope this helps someone too!

Sincerely,

Jon