mx5cartalk.com

Yep, it's a standard feature to sound a bit like a diesel truck at times. The Americans refer to it as gear rollover.

Then there is the growling/rattling noise that sometimes comes on at lowish RPM in 1st or 2nd gear when the car is hot...

yep, our first of the NC's has been doing it since day 1, nothing to worry about, there's nothing wrong with your clutch or gearbox

MX5's have always had quirks, this just happens to be the quirk owned by an NC

mind you, I don't think JBT has been up close & personal to many diesel trucks, sounds nothing LIKE my diesel truck

I am assuming you bought the car new so was the noise there from new?
If not, try depressing the clutch when it is making the noise (in neutral) and release it very slowly and see if you still hear the noise. If not it could be a faulty thrust bearing and Mazda will need to replace it under warranty.
If the noise remains the same when releasing the clutch slowly it could be a normal noise as previous posts have indicated.

I had a similar noise in my MR2 and Toyota replaced the thrust bearing and it was ok for a while but the noise eventually came back so I just put up with it for over 10 years til I sold it. It didn't seem to get worse or cause any damage.

The noise in mine varies with conditions. Virtually inaudible when the car is fairly cold but easy to hear when it has been run well on a hot day just prior to shutdown in the garage.

See this thread from the US forum: http://forum.miata.net/vb/showthread.php?t=292729&highlight=gear+rollover+noise

you'll also find that the noise is WAY more audible with the roof up, as are most other driveline noises in these cars.

I quite like driving roof up once in a blue moon, sounds & feels more raw to me.

cwcarruthers wrote:Thanks for your help guys. Not so much wiz043, just kidding :-)

I was about to post a "thanks, nice to know it's nothing to worry about" reply... but now I'll go check if the noise is still there if I pull the clutch out really slowly and get back to you...

Thanks,
Chris.

Ha-ha----fair enuff! My noise was only when at a standstill and not when going through the lower gears whilst driving.

If the 'slow clutch' trick doesn't make any difference it may well be a MX5 quirk.

cwcarruthers wrote:I wonder if Mazda's gram strategy means that this is something that is normally concealed in other manual cars with sound deadening material that the the MX-5 simply doesn't have?

It's a combination of minimal sound insulation AND the fact you are sitting right next to the gearbox.

The gearbox noise gets even louder if you add a PPF brace as I did, although as AJ says the noise is much less noticeable with the roof down - which is 95% of the time for me.

A PPF brace is a triangular shaped brace that is bolted to the rear subframe and it's purpose is to reduce drivetrain shudder (I think) ??

Drivetrain shudder in an NC?

I may be wrong about it's purpose----my wife says I am wrong about everything, but ask zombie.

JBT wrote:Drivetrain shudder in an NC?

You really need to drop the clutch sometime JB and stick the boot into it.

But mine's got traction control.

I got the PPF brace as part of the 5-piece I.L. Motorsport set - the purpose of the entire set is to stiffen up the chassis - and it made a huge difference. I already had coilovers and swaybars, I don't know if the difference would be as drastic on an otherwise stock car.
Many people on the "big forum" (miata.net) seem to leave off the PPF brace (to reduce noise) and just bolt on the other 4, but I wanted to maximise chassis rigidity.