I'm having a similar intermittent issue with mine, posted a thread on it in here.

If it helps at all, have a listen to this:

http://www.youtube.com/watch?v=i8-BlR_wPmU

Mine seems to be much better after a tank of 97 octane fuel, it looks like it might be bad supermarket fuel thats causing it for me.

 

When you take off at low rpm it sounds like a cow - just sayin heh .


Something to try :
remove the vacuum line going to the VFAD and see if the noise alters .
then try removing the vac line to the ssv and the vdi .

Sounds like something flapping around in your intake to me

 

Hey Brettus, if you look back to last page you'll see that one of the involved vehicles had the intake valves replaced.
Manic Mechanic, what was your engine temperature? High like the others?

This is really starting to sound like a cooling issue to me... Water or oil... There aren't that many systems left to consider

 

Tag for me having the exact same problem.

I just noticed it on my way home today. I redlined a couple of times and afterwards when getting to about 5k rpms it started making that same noise, along with a loss of power. I have an AP midpipe and a CAI. The engine was replaced with a 2007 version with roughly 35000 miles on it. I have no idea what could be causing it either, and I was leaning towards a cooling issue myself, but I just don't know.

 

Citrik - Got a recording of the noise you're talking about?

 

Actually I'm about to head to the store in a bit. If it's still doing it I'll record it and upload it when I get back. But it's the exact same sound as kd7gab's car.

 

Just want to confirm Im listening to the same thing you guys are complaining about.

 

Fair enough. It's uploaded right now. Just waiting for it to finish processing. It's kind of hard to hear on my phone but it's there if you listen close.

 

Have any of your locals listened to it? You got some smart guys down there in Columbus.

 

I just bought the 8 a few months ago, and honestly haven't had time to meet any other owners yet. My friend was in the car with me when it started doing it, but he's not sure either what could be causing it.

 

OK here's the video. You can hear the crap sound at about 5k after I shift into second. It sounds louder when you're actually in the car obviously, but you get the idea.
http://www.youtube.com/watch?v=JfSKF0WJL7s

 

I've always thought it was heat related, it just felt like hotter days the problem worsened.

Today it's 7 degrees - engine temp needle at the "warmed up position", Intake temp 11 degrees. Water temp 75-85 degrees. First time I haven't heard the noise in MONTHS! car had some oomph back.

I was going to do the throttlebody bypass this weekend but didn't get around to it. I'm going to go on a limb and say it'll likely help a lot.

Possibly a coolant flush as well.. though aren't modern cooling systems supposed to purge air on their own?

 

Do you even know what the coolant throttle body bypass does?

Purge air...yes...refill itself...no.

 

If you are suspecting this is a heat related issue (as I am) the first place to look is the cooling system. Change out your coolant with an appropriate antifreeze dilution for your area. (More is not better) Check your thermostat. Check that your fans operate properly.

 

@darkbrew: The engine has been running at least 15 minutes and is at the normal half way point on the gauge for me when the problem happens. Worse the longer you drive.

Someone on the UK RX-8 owners club is having the same issue as I am and has seen an intermittent problem with the front O2 sensor on his diagnostic kit, but it's not putting the CEL on.

 

Well the dashboard gauge is truly useless.
You'll need proper data logging equipment to get good data
Does the issue change with ambient temperature like some of the others?

First I've heard someone tying this to the O2 sensor...
But messed up AFR would do it...

 

Yeah, my ecu reader showed a 15'c change in temp reading at idle and no movement on the gauge at all! Coolant temps weren't very high, say 93'c max indicated. Ambient air temp doesn't seem to have much impact on the problem.

When mine chooses to misbehave and rattle, the mpg and power drop noticeably, so it could be AFR related I guess.

 

Id pull your front O2 and see what it looks like. Im thinking it is going to be pretty gummed up.

 

THis is definatly Ithe sound I've been having.
I too have a typhoon intake on it... As far as the exhaust I replaced my stock cat thinking it was gummed up with an exoticspeed cat. There was no change to the sound.

2 days ago I replaced my plugs wires and coils (oem for coils, NGK for plugs and wires)
it definatly helped! Now it only makes it aroung 6K and up after I've been hammering it....

I definatly think it's coolant related... most likely bubbles as I've been having to add 2 cups of coolant every 2 months... Going to flush the system this weekend and see if it improves.

 

Apv

 

APV?
Too easy... It cycles when you shut off the ignition (you can hear it right after the SSV valve test) and will trigger a CEL code if the travel sensors are not engaged.
Of course we can't rule out that the ports could be clogged up

And then there's my SSV issue which had no CEL... just a power loss

 

Forgive my ignorance, but what's the APV?

Fuel vapour purge valve?

 

No... but we do have one.

APV - Auxiliary Port Valve
Opens above 6250rpm to allow additional airflow through the aux runners.

 

Ah, cheers!

 

BLAH! ASHFIOWHEFLHWE THere are no words to express my frustration at this problem... I replaced coils, plugs and wires a week ago and the car ran beautifully! I didnt redline it a ton while driving, and it ran beautifully! Then today this kid wants to race, so I gun it a couple of times and the friggin problem comes back... SON OF A *****! Are we not supposed to redline the AT?!? WTF!
God is this annoying, I just wanna drive it with spirit and I cant... gotta baby the dam thing.

Why does the problem not present itself until I redline it?!? If my APV were to get stuck open, would that limit a decent amount of power, and change the sound!?