13...give us some specifics because I'm getting a "whirr" sound, at a very particular speed, in my XF. It's not the exhaust in my case, frankly, i'm not sure what it is.

I just noticed it last week, and I gave it a little test the other day to see if I could reproduce it...yep...everytime.

Here's the scenario. I'm accelerating and when I approach about 77 mph and I start hearing this whirring sound from the rear end. I lift off the accelerator (i'm slowing now) and it and it goes away. Accelerate and it starts again about the same speed. If I accelerate past about 83 mph it goes away, if I then lift off the throttle and decelerate back through the same mph range it's still there. I guess it's some sort of harmonics effect or something. It doesn't sound too awful or bad. Is this anything like what you're hearing/experiencing?