Noise in back at high speed

[lmacka]

No, this is not related to the post just below :-)

I'm hearing a noise that sounds like vibration/rumbling coming from the rear of my SWB Pajero J-Top '92. It only seems to happen at high speed (80k+) and comes and goes. Sometimes I can't make it do it but other times I can quite easily. It only occurs when the vehicle is "planing". Ie, I've accelerated to a speed and hold the accelerator still. While the vehicle's cruising along at that speed, I can hear the noise.
If I adjust the accelerator, it'll go away until the vehicle slows/fastens to the new speed.

It's not a whining sound and thus I doubt it's my pinion bearing. Doesn't seem to be related to heat or terrain. It doesn't seem to affect speed or make any vibrations, but it's bloody annoying!

Any ideas?
Someone suggested I launch a full-scale assault on everything that moves on my truck with a grease gun. I'd like to avoid that if possible

[jop]

copied this from the other post -
"Right, perhaps I'm doing my maths wrong. I have a set of Merit ATs on there. P245/70 R16
The spare (now on the front drivers side) is LT235/85/85 R16. It was on the back but I shifted it forward thinking it'd be slightly better there until I can get a new set. My logic was to take it off the axle receiving the power. Was i right to do this? "

How long did you run the larger spare on the rear?
As you may have done some damage




245/70R16 Overall Diameter: 29.50 in 749.3 mm
235/85R16 Overall Diameter: 31.72 in 805.68 mm

[lmacka]

Err, I'd like to say just a few Ks around the city but I popped the tyre up at Seventeen Seventy and had to drive home from there with it on... About 600Ks at about 110km/h.

I've been trying to find another car to borrow today as I have to drive up the coast in an hour but couldn't find anything. Reckon I'll be alright with it on the front?

By the way, this sound coming from the back was happening loooong before any of this happened.

[jop]

You should have an open diff in the back because of the locker - so it should not have caused an damage.
Still not a good idea though, best to get the right size asap

[lmacka]

I discovered today that the noise is coming from my u-joint. Thanks to klrevo for pointing that out for me.

Replacing it tomorrow.