High pitched wine on tourer

[kevrandle]

Hi, I have an annoying constant high pitched whine from the back of my:

Rover 75 Con Se CDTi Mk11 Tourer , 2005. It started after I disconnected and reconnected the battery, it is constant pitch and volume and is on all the time, even when the ignition is off.

Thanks.

Update: I disconnected the battery for a few hours, then reconnected and it had mended itself!!