Now this is really interesting - if indeed the "thunk" noise is a faulty rear damper, that may explain the "PASM failure" message I experienced a few weeks ago when my suspension went into failsafe mode. I figured it was an electronics glitch, but I guess the electronics could in fact have been telling the truth.

Which dealer are you using? - Porsche East London couldn't find a fault when I took the car in last time (early March).