Just got my XF about a month ago. The car has 48k miles on it. This happened to me 3x over the weekend. When the car was cold I would accelerate from a stop to the left I would get a loud clunk. I was not positive if it came more from the transmission or rear end. I tried rolling the windows down but of course it quit once the car warmed up some. Did not happen when turning to the right and did not happen after the car warmed up.

Has anyone had such an issue?

 

There's two options for this in my opinion: engine or transmission mount, or something in the rear drivetrain/suspension, although it'd be a little surprising if the sound completely disappeared when the car warmed up I guess it's possible. I'd see if you can replicate it at low speed with someone stood outside the car to get a better idea of where the sound is coming from.

If it is drivetrain mounts, there are 3 mounts for the engine/transmission: one on the left of the engine, one on the right, and then one at the rear on the transmission. I've changed all three of them (if your car has been in hot climates they're likely to need it as the rubber seems to dry out and perish) - you ideally need a lift with a transmission jack although it's certainly possible with the car on axle stands. The easiest one to change is the transmission mount at the rear, the access to the mount on the right side of the engine is a pig but the left side one is even worse as you have to remove the AC pump which has solid pipes going to it, requiring you to drain and then refill the AC system.

In terms of rear drivetrain I'm less experienced with, I guess it could be a CV joint on a halfshaft going, or maybe issues with the differential locking motor?

 

Thanks for the writeup Dave. That's interesting about the motor mounts, assume they go bad pretty quick if you have already had to change yours. What sucks is TODAY it didn't do it. I am going to have to put some more effort into seeing if I can reliably recreate it every time.

I also read on here about a gas tank thump that can happen but it was mostly upon deceleration I believe.

I still have about a year of CPO warranty left on this car so it sounds like if I can recreate it then I might need to go to the dealership because it sounds like those are things they might replace.