I have also managed to contract this problem just after it had been in for a service, sounds very much like its coming from either the suspension, rear axle area or anti roll bar when me and my partner investigated. Speed bumps were the main reason I noticed and over the recent weeks and its just got worse. I have a 64 plate M7.5 Fiesta ZS and she's currently booked in at a ford dealer for this issue fixing under warranty, glad it didn't happen just after end of this year though or else warranty would have run out :S. Ill be back to report the findings of the employees of Skipton Ford now that I've found this thread. Been looking everywhere for answers for this!!