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

by in Niagara Falls, NY on October 28, 2013
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2 answers 4 comments
ANSWER by , October 30, 2013
What about coasting in neutral at 45-50 mph? Rule in/out drive train.
COMMENT by , October 30, 2013
when I do that it is silent
COMMENT by , October 30, 2013
Have rear diff. checked/serviced first , then trans. Is it all-wheel drive?
COMMENT by , October 30, 2013
yes all wheel drive
ANSWER by , October 29, 2013
ck for vac leak at intake manifold
COMMENT by , October 30, 2013
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.