What's this on an XF

[Polome]

Recently had use of XF saloon and sport back , both automatic diesels. Never driven a modern diesel before and was very impressed. Fast enough and serenely quiet ( compared to my 997 that is ) they were great family cars. Having a good look around it I noticed a cylindrical steel tube hanging off the back of the diff. It intrigues me what this can be ...anyone know what this is? Thanks.

[Polome]

Thanks for the info...do you mean it's just a lump of steel bolted on for weight or does it have a more technical function? Regards.