On my 1991 I just got there is a bit of a chatter noise when the clutch is engaged in neutral when the car is sitting still, when the clutch pedal is pushed in, it goes away. Also there is a loud chatter/grinding/whirring noise upon deceleration from about 4K to 3K rpm mainly in 1st 2nd and 3rd gear. The noise disappears immediately when the clutch pedal is depressed. The clutch was replaced by Woodhouse Mazda in Omaha, Nebraska within the last year(I wasn't owner at the time) so I don't know if it did it then too or not, but it has done it all the time I have owned it. I thought it might be the Cat, as have had a similiar deal in a previous Mazda MX-6 I owned, but the noise just doesn't sound like it could be from vibrations in the cat...also because the chatter at idle too that goes away when the clutch is pedal is pushed in makes me think the two sounds are related...any ideas.

Thanks in advance

 

what type of clutch/flywheel?

 

oem I would imagine...as it was done by the dealership

 

It's not uncommon. Mine chattered like a bitch. lightened flywheel and ACT clutch. I pulled them both, resurfaced my OEM flyhweel and installed another clutch kit and it's gone.

But if you search miata.net, you'll find lots of similar complaints.