So, travelling to work today and I noticed a whine coming from the back. It was still there coming home. A workmate I was taking home noticed the same whine and asked if it was the diff. He mentioned something about a head plate?
Not sure, but, anyone got any ideas? Had the same symptoms? It is most evident at 100km/h and reduces in pitch with reduction in speed.
I had a quick look in the service manual, but can't find anything.
I change the diff oil approx every 20,000km.

What diff oil do you use

The recommended SAE 90 by Castrol.

You sure it's not the tyres? Just a thought... Diff whine noise would be very apparent under acceleration/load at speed?

Quite sure it's not the tyres, they are only 10k old

Have you been using proper LSD fluid, I personally use diaqueen from Mitsubishi

Yeah, it's proper fluid, I'll check again.
I'll even give the Diaqueen a shot, see if it makes a difference.

Once the damage is done nothing will fix the noise unfortunately. I generally would not do changes every 20k personally but then again the only downside to doing this is that it costs you more.

May just be a case of bad luck perhaps, even if you did not use the correct fluid this would have more effect on the clutches in the LSD than the bearings or the crownwheel and pinion.

When you did the last change, what was the condition of the fluid.

The fluid came out clean and same colour it went in. No indication of any flecks or chunks. On the weekend, I'll get under the rear and check all the mounts and condition of it all.

FWIW, changes in pitch are also common with worn bearings and tends to be there regardless of load (acceleration/coast/deceleration). Diff whine tends to come & go with changes in load.

Mine has the same noise. I first noticed it after having the gearbox flushed and diff oil changed by a Mitsubishi dealer. After that I changed the diff oil again myself but there's no difference.

Mine whines a bit on overrun from 100km/h between about 95 and 75. If I pull it back to 4th or 3rd I don't notice it but the engine noise is greater so that maybe disguises it. I get the feeling mine will go like this for years and I'm not concerned.
It never whines at any other time. In fact now I think about it, this kind of whine is diagnosis of crown wheel and pinion mesh pattern. Certain situations cause whining at different times.

How loud is it really? They all do it ever so quietly. If your radio is off and you are driving slowly you can usually hear it. If that's the case then its nothing to worry about. If you have come from a FWD magna, you will find that the AWD's are no where near as quiet and smooth and you will hear noises you are not use to hearing.

GTPete laid a few sheets of dynamat under the rear seat, all but removed noise from the rear diff

GTPete laid a few sheets of dynamat under the rear seat, all but removed noise from the rear diff

I have some left over dynamat, but, worth a shot.
Temp solution till I can get it sorted.

I had what I thought was diff whine in mine around the 60-80kph. Did the oil change thing, no change. Then a mate said it might be the tyres. I had Bridgestone Grid 2"s with approx 12,000k on them. Swapped the rears from the mates AWD Verada which were near new Dunlops, took it for a spin, no noise.
Put new tyres on it, all good.
Woth a try.

Huh! I got Bridgies on mine too. You've got me thinking.

I had some Bridgestone ER300 tires on my Mazda 3 (OEM tires).
They eventually started making so much noise that I was convinced there was something wrong with the car and took it for a warranty claim.
Anyway, they said it's the tires, but I didn't believe them. Got a set of Michelin PS3 and it's smooth and quiet.

Moral of the story, tires can become unexpectedly loud.
If your front tires have better tread try swapping them front to rear to see if there is any change in noise

Yeah I've done that. The front toe was too far in and was rubbing the outside shoulders so I swapped them front to rear. The rear (diff?) whine was unchanged.

With tyres, certain tread patterns develop a hum. The Bridgestone Grid 2 and ER300 are both notorious for it. Had them both before. It was almost like driving a 4WD with mud tyres.

Grelise, you have extra wide (245) tyres which will generate more noise than narrower tyres, and depending on the tread pattern of the Maxxis, will generate more at certain speeds (harmonics). Try swapping at least the rears (preferrably all 4) for some 235/18 or 225/17 tyre/wheel combinations (with non-aggressive tread patterns) and see if the noise disappears.

Thanks guys for the ideas, i'll take them in and go from there

Ok, so I'm changing the RH rear bearings, got as far as taking the castle nut and caliper off.
How does one then proceed taking the disc off.
Yes the handbrake is off. I have tried tapping the edges while pulling the disc. The drive shaft moves freely also.
Any ideas?

Got the disc off, have undone the 4 bolts holding the bearings. Is it now supposed to slide off or is there another bolt?
Looking in the service manual suggest it has only the 4 bolts then just slide off hub and bearing together.

You often need a puller as they will be fairly tight to remove

I had what I thought was diff whine in mine around the 60-80kph. Did the oil change thing, no change. Then a mate said it might be the tyres. I had Bridgestone Grid 2"s with approx 12,000k on them. Swapped the rears from the mates AWD Verada which were near new Dunlops, took it for a spin, no noise.
Put new tyres on it, all good.
Woth a try.

The first time I ever noticed any diff whine was when I upgraded my wheels & tyres back in '08. The whine is noticeable just on 100kph on throttle, it hasn't gotten any worse & it's not particularly intrusive, so I don't worry about it.
With the exception of my beloved TJ1.5 magna exec, I have driven rear wheel drive cars most of my life so I'm somewhat used to having some diff whine.

I change the diff & transfer case fluids every 2 years which amounts to around every 20,000 - 24,000 kms.