[MrWill75V6]

Though not on a Rover, I had this issue on my old Skoda. The garage didn't seem to know why or be able to do much about it. The longer it went on with the car driving normally, the less it seemed worth the possibility of being advised an expensive repair was required, so it got left for 1000s of miles and never really caused a problem. Not advising that this is the best approach to take but that was my experience.