It is most likely a bad bushing. You will have to carefully look at the bushings for the different rear suspension pieces. It could be the sway-bar links. You need to see if it has any play in it, although I think they usually cause a "pop" noise when hitting bumps.
Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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