clunking noise in 92 suburban

I have a 92 GMC Suburban. When I am driving I hear a slight rythmic clunking noise. It only does it when the vehicle is in gear and moving. I have shifted
into neutral while driving and the noise goes away. I can't pinpoint any area where it is coming from. I checked underneath for sloppy ujoints..they seem to be fine. Does anybody have a suggestion as to where I should start? Any help would be appreciated.
Thanks, Dave
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clunking
shifted
area
seem to

be
2 or 4WD?
Doc
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OK, does it make the noise in both 2 and 4wd?
Doc
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My guess would be a front cv joint, mine did the same thing.
Tim

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I don't use the 4wd. When I bought it a couple of years ago, it seemed to not be quite right in 4wd.
I put the back up on jack stands, and when I run it in drive and overdrive it makes the sound. It could also be described as a helicopter sound. It sounds like it is at the rear differential, but the sound could be just traveling down the driveline. It does not make a sound in reverse, first, or second.
Dave
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what say you Doc?
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not
it
sounds
down
I'm thinking.....sorry bud. I'm trying to figure out if it's NOT making noise in R-1-2 because the driveline is moving more slowly than it is in 3-OD, or if the noise is coming from the tranny. Have you pulled the rear diff cover to see what's going on in there?
Doc
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