Noise from rear of car?

Any mechanics or guys who play one on TV - I have a problem for you. I have an 04 astro van AWD. It makes a noise from the rear when you raise or lower the rear of the car (ie on the gas or brake) It is like a clicking/rubbing sound (better yet, it's like a zipper sound - like raising and lowering a zipper. I jumped on the bumper and couldn't replicate it, but it was storming/snowing so I didn't give more than a few jumps.

Anyone have this before? Rear shocks? Rear Leaf Springs? Doesn't seem to be just braking, cause I can make it happen with the gas from a stoplight...

I'd throw a jack under the differential and jack it up and see if you can narrow down the area of the sound. If you're hearing it upon acceleration and braking, my guess would be shocks.

Could a number of things,rear end low on fluid or needs more limited slip additive if it's clicking it could be either a pinion bearing or diff bearing worn in the rear end thats causing a chattering sound or i'v also known of the blazers an astro's leaf springs chatter when the rubber washer/spacers wear out in between the leafs.

Dont forget to check the U joints on the drive shaft and if it's AWD check the front shaft also just to make sure they'er not trashed, Im assuming it has rear drum brakes, So you could write off the rear brakes chattering because drums either work or they dont. No dragging there..

I feel relieved. The noise is the rear heat shield rattling when the van goes up and down on braking and acceleration. Easy fix for a change!