Regarding my noisy diff, I've been looking at the picture's of the contact patch I took when I stripped mine down and the contact patch looks way off,  the drive side of the wheel is fine but the coast side looks out, I'm assuming from what I read that both drive and coast patches should be similar size, shape and position ?

I've done cars and trucks, but never a UTV.  I'm assuming its the same.  The most important factor is that the contact patch is somewhat on the middle of the tooth.  It can be forward, back, up or down, just not off the edge of the tooth. Or too far down in the base.  The coast doesn't have to match the drive as long as they are both somewhat centered.  Hope that makes sense.  Don't waste your time with gear marking compound.  Use hand lotion.  Hope that makes sense.  Are the ring and pinions adjusted with shims like a car?

Ok thanks, the drive side is near the centre, coast is  right on the toe, yes they are adjusted with shims

I would be more concerned with the drive side. As long as there is no play in the pinion or carrier bearings allowing it to pull in and push out when on and off the power coast side should be good I think. I also am not familiar with these particular diff,s I'm going on car experience.

if it wasn't so noisy I would leave well alone, I'm not sure what's causing the noise but it's making it on both coast and drive, I would really like to find the cause

they are all whiny. To me it seems more like in the gear box than the diff but I have never looked into it.

Ok, as it's not a big job I'm thinking about removing the diff and having another go at improving the contact area

[2015 Z Force 800 53/Trail EPS]

they are all whiny. To me it seems more like in the gear box than the diff but I have never looked into it.

Some supporting observations on my part for this is that when I went to the Castrol Power-1 over the conventional I was using in the engine, I did notice a strong reduction in the overall "whine" of the drive train. This was without changing any differential or gear case oil, just the engine oil which to me at least.. means some of the noise is coming from the transmission's gears.

I think you may be wasting your time Dave, see NKM's comment, further evidence that the diffs are not making the "whine". If of course you have the same whine everyone else does. The whine these makes just never sounded to me like diff noise, diff gears usually make more of a howl and they change when you are on or off the power, usually making the most noise in my experience when there is no load on the diff. The whine these makes sounds more like a straight cut gear whine. That being said, I have no idea how the gear box works in these but that is where my gut said the noise was from.

Ok, thanks guys

I returned my Zforce 800 a week after I purchased it as I told them I could not tolerate the noise from the back end.  This Z was my second SxS so I knew that noise wan not right.  I took the mechanic for a ride and he confirm the noise and actually said it sounded like a wood planner especially while accelerating.  I left it with them and returned a week later.  Now I am no mechanic but they told me they ordered in some new shims as the diff was too tight. I took it for a test drive before leaving and the noise was no longer there.  5000 km later and still no noise   :-)

[2015 Z Force 800 53/Trail EPS]

I returned my Zforce 800 a week after I purchased it as I told them I could not tolerate the noise from the back end.  This Z was my second SxS so I knew that noise wan not right.  I took the mechanic for a ride and he confirm the noise and actually said it sounded like a wood planner especially while accelerating.  I left it with them and returned a week later.  Now I am no mechanic but they told me they ordered in some new shims as the diff was too tight. I took it for a test drive before leaving and the noise was no longer there.  5000 km later and still no noise   :-)

That is good news. Besides the transmission there really isn't anything else that can make that noise other then a mis-adjusted ring and pinion. Some have reported theirs tight where mine seems loose (excessive back lash) and when I change my diff fluids, while the front's magnetic plug is almost clear of any shavings, the rear always has a good stack of shavings on it.

I barely use 4x4 i would expect my front diff fluid to be pretty clean as well. 

I change the oil regular and no sign of any shavings in mine either so I'm happy she's not eating herself, from what I've seen my pinion and crown wheel are not adjusted right. The contact patch's for coast and drive are much different on mine, I understand they should be similar in size and position.
When turning my diff by hand you can feel each tooth engaging although it not bad it's also not smooth either.

I change the oil regular and no sign of any shavings in mine either so I'm happy she's not eating herself, from what I've seen my pinion and crown wheel are not adjusted right. The contact patch's for coast and drive are much different on mine, I understand they should be similar in size and position.
When turning my diff by hand you can feel each tooth engaging although it not bad it's also not smooth either.

The terminology is throwing me off a little bit. The "crown wheel" I am assuming is what I would call the ring gear. The mated ring and pinion. I cannot see how you would be getting a pattern off from drive side to coast side unless you had a bad bearing allowing the gears to suck together on deceleration. I am not an expert but I do not see a way that you could set the lash to adjust the drive side and not affect the coast side.
I agree if you feel it being chunky when you turn it something is going on, but are you sure you are feeling each gear contact or could you be feeling the each roller bearing in a diff bearing?  Be sure you are getting no movement in or out on the pinion or side to side on the carrier.
The other thing that would be strange is you say it makes no difference whether you are accelerating or decelerating for the noise. If the gears were moving under decel or accel the noise pitch should change as the gears got moved closer and further apart.