i made a similar thread on the miata subreddit but i'm casting my net wide here in hope of some wisdom
Video showing the noise with the car on jacks;
This noise has been present for around 6 months and has been slowly getting louder over time.
I did a differential fluid change but there was no change in sound (that video was taken AFTER a diff fluid change). Although during said change i noticed a few very tiny metal shards on the magnetic plug and the oil did have some silver swirls. This differential was an LSD from the first year of the newer design lsd (Tochigi-Fugi unit)
the transmission fluid was changed about 10 months ago and the removed fluid didn't look bad.
I checked for wheel bearing noise but i don't think that's it, neither of the drive wheels make noise when spun by hand and neither are wobbly.
i'm kind of hesitant to drive it now out of fear of potentially causing further damage.
what should i do to diagnose this?
note: the noise depends on speed ONLY. it doesn't get louder or softer while under acceleration or deceleration beyond just generally getting louder the faster i go, and it doesn't go away when in neutral or with the clutch held down

 

Move your ear closer to the noise until it stops getting louder. The noisy bit is the broken bit.

It's very common for those diffs to fail.

 

well fiddlesticks up my poop chute.
i assume repairing the unit isn't as cost effective as getting a used replacement? Ebay has me disheartened with replacements hovering around $600

 

So you want to replace a 15 year old diff that frequently fails with another 15 year old diff of the same design, with unknown mileage, from ebay, that will likely fail? No. Just No.

If you want to stay with a LSD the reliable option is the torsen style diff.

 

Sounds like a bad diff to me, bearing noise from a failed carrier bearing is my guess. If the metal circulated around in tiny spec, gears are probably ok. If there's pieces, the face of the gears could be damaged. Likely could be rebuilt, you would have to disassemble to inspect and see what's bad.

I have a used diff in the classifieds for cheap that doesn't make any noises (MSM torsen, strongest torsen for a miata), but you would need MSM axles to run it. There is a guy on m.net that has them paired with a more expensive MSM diff he has listed for sale.

 

well, i'm short on cash at the moment so i think i'll have to swallow my mod desires and pick up a regular open diff for the time being for presumably much cheaper

 

Where are you located? I have an open diff that I need to get rid of.

 

Central massachusetts, just updated my profile information for that
quite a ways from washington state unfortunately

 

my friend has a VLSD from his 90' that he parted out, we are in western mass if you are interested.

 

i'm not sure if that'll bolt up to a 2003?
also weren't the early LSDs kind of problematic regardless?

 

cast 1 net in 1 thread in 1 section.

 

It won't and yes they are.

Slap a torsen in your existing case, call it a day.

 

or buy an open for pennies. I've seen them for $50

 

would very much like to know where.
ebay?
craigslist part outs?
craigslist solo listings for just the diff?
facebook buy/sell groups?
the differential fairy? (totally real, by the way)

 

I paid $60 for a complete 4.30 open assembly, including housing.

I'd offer to sell you the guts, but it would just be the carrier itself. Dumping an MSM carrier in with the 4.30 R&P for..... things.

 

I would say a WTB thread on here would be an excellent start. The kind of people that are active on a turbo miata forum are the kind of people who sell open diffs. Plenty of members in your area as well.

 

well, i created one
also created a WTB on the new england miata buy/sell facebook group

 

@Ridethecliche has an open diff that he wants to get rid off. Also in Central Mass.

Hell, I also have an Open NB1 diff that's going to be lying around pretty soon. 50$ and its yours.

 

Well, i purchased Ridethecliche's open diff, now to just work up the motivation to do the exchange!
if that doesn't solve this issue i'll be shocked