I was hearing the same clunking noise, front driver's side, on my 500E, and I took it into the shop today. Up on the lift, plain as day the left bushing on the sway bar was torn and not in the mounting bracket. My tech has ordered the part (apparently the replacement kit has four bushings) and I will have it repaired tomorrow.
Are there "bushing-gremlins" about?
Make it a Good One!