high pitched whining noise on 2004 Jeep Grand Cherokee

this noise comes and goes depending on throttle pressure under heavy load and acceleration it goes away, But under coast or light throttle it has an annoying high pitched whine hard to tell if transmission or rear end

Asked by for the 2004 Jeep Grand Cherokee
ck for vac leak at intake manifold
thing is the 6 cyl engine runs smooth I do not hear a leak when it is just idling and to hear one at 100 klm it would have to be really bad I would think. At a 100klms if I let off on the gas and then apply just a little the whine comes back depending on throttle pressure.
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1 more answer , 3 more comments
What about coasting in neutral at 45-50 mph? Rule in/out drive train.
when I do that it is silent
Have rear diff. checked/serviced first , then trans. Is it all-wheel drive?
yes all wheel drive