I noticed when I had the stereo down that there is a very slight metallic sound each time I rev the car to about 6K rpm's. As I go past 6K the sound stops so I don't think it is pinging or anything like that. My car has about 3200 mile is this sound normal?

 

mine does it too. it sounds like a metal whirrrrrrrrrrrrrring sound.

it does it on 87 and 91.

 

I asked about this same exact thing I believe and the answer I got is that the noise is another set of fuel injectors going. Sorry I can't get any more technical than that because I don't really know how it all works. Just good mazda engineering I guess.

 

search my posts for theads titled S-DAIS your answer is in there

 

I searched and found several entries for S-DAIS. But none of them were conclusive enough to make me happy. Are you saying that the S-DAIS is the culprit for this popcorn machine under the hood??

 

I know EXACTLY what you are talking about! To me, it sounds like ~6k is the resonant frequency of some sheet metal part. When you hit 6k rpm, it resonates and makes that metalic rattling sound. Sheet metal parts have light damping and so the response is very narrow around 6k. You don't hear it much above or below that rpm. To me it sounds like a heat shield or something. I had the same problem on my old 240sx.

 

at 6250 rpms the tertiary intake ports open. there are little barrels inside the trac which rotate to open the port. the sound you are describing at the rpm you are saying suggests that what you are hearing is the barrels rolling to open.

 

Actually, I hear the rattling sound at about 5500 rpm. -> not the ports...

 

I have this noise as well. I am under the impression that the M-Flash will take care of this. I plan on getting the flash with my next oil change pretty soon.

Read more about it here.
http://www.finishlineperformance.com...01-022-04.html

 

at 5500 the VFAD can open under certain loads/throttle positions.