I have the same spring and pop/clunk but mine comes from the drivers side. Mine doesn't "boing" going straight, only when I'm turning into/out of my driveway or turns over bumps and uneven roads.
I've been wanting to take my van to Agile to have them give it a once over, but the only time I'm down there is usually on a weekend, so it's been a challenge.
2005 E350 Chateau - V10 - Agile Offroad 4x4
2012 CTS-V Wagon - For the baby...