Hi - I'm a new member to the club and am a Jaguar 'pensioner', having worked at the X type assembly plant (Halewood) from X Type launch in 2000 though to my retirement in 2005, and was involved in this issue during quality testing in the plant. First of all don't panic, and there's no neeed to stop using the car, the noise you are hearing is 'prop shaft moan', and unfortunately does manifest itself when the temperature drops to around freezing point. We thought we had contained the issue within plant, but obviously we didn't ! The issue was down to the supplier making changes to the prop shaft universal joints, without full verifcation of the engineering change, and more importantly, without informing Jaguar !!!! You can fix this by (I know this sounds a bit obvious) by either swopping the prop shaft or the U/J's, either with a pre or post 2005MY prop - hope this helps - Cheers!