First off, in seaching, I found one thread that had some pertinent information: https://www.miataturbo.net/forum/t33852/ and the following quote is from it.

I have the same bushings installed from the master kit I bought (also have MazdaSpeed Miata engine mounts), and I have noticed that from about 45-50mph and up, I can also hear a whine, it's seemingly RPM based, and is only present when my foot is on the accelerator. No gas = no noise. I haven't been able to pinpoint it's location, but my assumption is that it's R&P/diff related. I can hear it with or without the tops because I know what I'm listening for, just easier to hear with the hardtop, it's not very loud at all. Anyone else have this noise? Is this an indication of a problem or just noise produced by the stiffer mounts?

I had my 3.636 gears installed by the same machine shop that did my engine work, they used the FSM, and reported no issues at all. ZX-Tex, if you see this, did you have any diff work done during your build?

And just as a sidenote, haven't really noticed any increased vibrations from the mounts, but my car was never really smooth to start with.

 

if its rpm consistent the rear end is not your problem. The same cannot be said for your retardation and homosexuality.

 

Right...

 

I'm guessing that the stiffer mounts are just doing a better job transmitting the noise and vibration that was always there through the car to you like a screwdriver handle pressed up against your ear when you are listening for engine noise. No gas = no noise makes sense as well. Sure, they are still turning but not being pushed so no noise. My tranny is whiney even without stiffer mounts. I'm sure it would be worse with the stiffer mounts.

 

I went to a different rear end at the same time that I installed the MMR diff bushings, so I do notice a lot more whine now, but I can't say for sure that it's all down to the bushings.

 

nice edit. I was just about to talk **** to you.

 

Yeah, I know. That's why I edited it out. I don't have time for the likes of you.

Thanks for the responses Stein and Koto.

 

If it makes you feel any better I recently installed a set of urethane diff mounts along with a 3.63 R&P. I have a whine similar to yours in the 50-65 mph range.

My car is not currently running, so I haven't had an official diagnosis, but the person who installed the R&P said its probably the mounts.

 

Its the bushings. I swapped my delrin ones out after a highway drive, ******* retarded with urethane motor mounts.

Stiff mounts= Teh noise!

 

I already noticed an increase in drivetrain noise since installing a (very) light flywheel. I can only imagine what a noisy, whiney bitch it will be with stiffer motormounts and diff. bushings