Lately I have this issue that came up...going over bumps I have this slight knocking sound coming from the rear suspension, and I also hear the same sound when accelerating from a stop, say, from a stop sign. Swaybar links and mounts are fine, I can't see anything else in the rear suspension that is loose or looks out of place...all I can figure is that my rear shocks are really worn, and need replacement, they are high milage KYBs that have been through a harsh life of cut springs...any suggestions on other things to check? This is a new sound I have never heard before, and it was hard to even figure out where it was coming from at first.
If a visual inspection does not find the problem, the best way to diagnose this complaint is to unload the weight bearing componets of the suspension.
1) Jack up rear, and support with jack stands. The rear wheels off the ground about 4-5 inches. (It is not recommended to lift the car from the differential on an IRS.)
2) Place floor jack under spring, and lift to compress the spring under the weight of the car, but don't lift the car off the jack stands.
3) With a long lead pipe, say about 4.5-6 feet in lenght, 3" o.d. or so, place one end of the pipe under the tire, and lift the tire up and down using the pipe as leverage. It helps to have an assistant while you go under, and look for parts that are moving in excess: worn or broken bushings, bolts, shocks, links, springs etc... Listen for any grunts, squeaks, knocks, etc...And the tire should move up and down without any binding.
4) Repeat on other side.
This procedure is also used to diagnose worn ball joints on the front.