Outer Limits 4x4 Board

on my 100 series 4.5L manual with 2inch lift with 30mm spacers at the front when i hit 100k or more when i back off on the throttle i get a growning noise with minor vibration which as soon as i put the throttle back on it goes away. toyota said dont worry about it as being constant 4x4 you will always get some noise but its a little too loud sometimes and something is not right. My local mechanic said dont worry about it until something gives as its too hard to diagnose but he seem to think it was the front diff. My friend with simular lifts in patrols had the same issue and it was uni joints but both toyota and my mechanic said my uni's are fine. i ended up putting a brand new front shaft with new uni joins and this has not fixed the problem and now people are telling me to check caster angles. If anyone else has experienced this please help cos i am sick of spendning money that is not helping fix the issue.

If anyone seriously can help and is in melbourne please contact me.