Help, squealing GQ

[bruggd]

Hi there, I am in need of some help diegnosing a loud squealing noise coming from underneath my 95 td42 coil cab GQ. I purchased the vehicle about 8 months ago, during a return trip from Alice to Melbourne recently a loud squealing noise developed, coming from underneith the vehicle it gets louder and increases in pitch as the speed increases. It only happens after driving for more than half an hour at freeway speeds, when I stop in a town for 10 mins it dissapeares but then reappeares further down the road. This leads me to believe it's a heat related problem. I have had no mechanical failures even after several thousand K's with this problem, it is fine while driving around town, no noise. So far I have replaced all fluids with correct specified, all uni joints, and front wheel bearings, the gear box is a re co from before I purchased it, it's not the throw bearing in the clutch. Next on my list would be rear axle bearings and or rear diff, I don't believe these are the problem though. The rear hubs don't get hot nor do they have any play, the diff works great now with the correct fluid. I am trying to eliminate using the cheapest first method. Any advice or experiences would be greatly appreciated. Thanks.

[Clanky]

Idler pulley bearing?
Loose or slipping fan belt?

[bruggd]

Unfortunately not as easy as a fan belt or pulley. Noise does not change relative to engine speed, noise does coincide with the road speed. Gets quiet down to a squeak when slowing down through a town. And makes no difference what wheels/tyres I'm using.

[ST391GQ]

Handbrake??
Maybe stuck on slightly...or a spring inside has come adrift allowing it to rub on shaft/drum. Or maybe has a lopsided mounted shoe in there with steel backing contacting moving parts.

HTH.

Cheers Keith