Gearbox/diff squeak, poor engine braking

[Kiz]

Hey guys, first post :)

I have an intermittent squeak, kind of like a belt squeak but coming from the gearbox/diff area. It only happens when the gearbox is warmed up. Its very noticeable when you turn the car off and everything slows down for that half second.
I changed the gearbox fluid to Royal Purple 75W-90 2 months ago.
I've tried clutch in/out when I can hear it squeaking (usually at Maccas drive through when the sound reflects off the wall) Clutch does nothing but change the engine revs ever so slightly which in turn changes the frequency that it squeaks (which is already very irregular, not a cyclic noise).
Gearbox fluid level is perfect, well it was when I filled it a month ago and the car doesn't leak a drop of anything.

I've done the screwdriver to the ear test tonight on the AC, alt and driveshaft but since the hearbox wasn't warm when I did it I couldn't hear anything from them.

I've noticed it does have more 'crackle' in the engine than usual (kinda like intense pinging but it's always done it) but only slightly more, couldn't tell if it started with the squeak.

I did fit a lightened UD pully in 07....

Today I noticed that there's no resistance when engine braking. Well OK there's a little bit but I attribute that mostly to rolling resistance. 2nd gear does provide better engine braking but 3rd and 4th it's like the car is in neutral. Acceleration is OK, I heard one loud squeak around 2000RPM in 2nd gear while accelerating mildly but it never occurred again.

I also swore I had a flat tyre today - uneven braking, vibration and mushyness... stuck my head out the window at the lights and they were fine! Couple of minutes later and it was back to normal. Maybe I'm going crazy


Don't think there's anything more info I can think of right now.
Oh it's an '06 LB 2NZ-FE 5-speed.

I've had spigot and GB bearings suggested as causes. Eliminated the throwout bearing as the clutch makes no difference to the squeak.

Thanks for reading, hope you can help