^it's worth trying first IMO. if you can't put it up on stands yourself, whip it round to a friendly garage and ask them to raise it on a ramp so that they can check tightness of the clamps that hold the rack to the subframe - check they're as tight as they can sensibly be, see if it sorts it. bung the garage a fiver or something
if it's not that, it'll cost, as something will likely need replacing
as said, this only seems to affect the RS cars with the hydraulic rack - don't know if you've electric in yours and/or the problem doesn't affect the cars fitted with electric racks. worth trying for the minimal effort/expense anyway