I have a rattle that is temperature, load, and rpm dependant. The noise only occurs once the car has been driven for several miles, is between 3,200 and 4,000 rpm, and when accellerating lightly. It seems like it only occurs in first and second gear. It sounds like it may be coming from the transmission, but is hard to pinpoint, especially since it only happens under load.

What is the failure mode for a 6 speed Mazda transmission? Are there bearings that tend to let loose before anything else that would cause the noise described above?

Full disclosure: The noise started happening after a hellacious first to second gear burnout that ended with egged rod bearings. Once those were swapped I noticed this noise.

I'm going to break out the Det cans and clip them on various spots, but figured I'd ask those more in the know; maybe this is how 6 speeds meet their end?

Sorry for the rookie question, but I have 0 experience with broken Miata transmissions. Put me in a VW with a noisy trans and I can tell you exactly what's about to let loose

 

6 speeds are pretty stout, I doubt its your trans. People have issues with burnt synchros in the 6sp's (and even that is not that often), but I've yet to hear of someone with under 400whp and doesn't track it regularly that destroyed one

 

IIRC ceo destroyed his at 350rwhp however he was really abusing it in street racing. 3rd or 4th gear, can't really remember.

 

I guess I should update my sig. I'm over 350 to the wheels now.

It was 35 degrees here this morning. I didn't hear the sound at all on my 5 mile drive to the train. This is driving me absolutely nuts trying to figure out what's moving around down there.

 

I would start by pulling the drain plug and see it you have any metal flakes on the drain plug. Tiny flakes are normal. Big chunks are not.

 

Im pretty sure if you have a stripped/shattered gear you'll hear it all the time, not just every now and then and at a specific rpm. It definitely lets you know when its stripped or broken. just my .02

 

Hmm, I'd pull the drain plug and check for crap... Could be anything :(

If ya need a garage to poke in, my place in sterling is open!

Cheers,
Matt