Knocking noise from rear - rear trailing arm ball joint/bushing?

So I've had this annoying popping/tapping/knocking/clunking noise for a while. It's coming from the rear and is VERY audible at speeds below 30mph. The frequency of the noise is very high, and occurs when driving down a flat street (the smallest bumps make the noise occur, large bumps don't really do it as much). I am thinking it is the rear ball joint and/or bushing on the rear trailing arm, as shown here:



http://ift.tt/14Huwp4



I jacked up the rear and got under the car and wiggled things around - nothing seems out of the ordinary. However, I noticed I can replicate the noise by repeatedly pushing down on the passenger rear quarter area (I think it's the same noise, probably sounds slightly different outside of car vs inside).



Now my question:



What is the best way to check this bushing and balljoint for failure?



Also, I've already replaced all of the common failure items, as indicated in Mango's thread for suspension overhaul, which is what leads me to believe that these bushings/balljoints are the only thing it could be....