I have a high performance vehicle do this recently. I had the tires balanced 3 times at 3 different shops. The tire belts must have gotten loose. I replaced the tires. Tires have a speed rating as well as temp and wear ratings. High speed at high temps will destroy a tire from the inside. Be careful.

 

Following up on what Marc said, I would recommend making sure your tires are round and haven't de-laminated. If they check out OK, then do a dynamic road balance and alignment. See if that helps. If not, I would then look at bushings and ball joints. I would recommend getting with a Jaguar trained technician regarding the balance and alignment as they would have the latest specs or techniques.

Good luck,

Mike

 

Consider getting a "Road Force" wheel balancing done. This will determine if the tires has any construction problems. If you have not heard of Road Force look at this:
http://www.gsp9700.com/pub/features/how.cfm

Discount Tire can do this but you might need to call around to find a shop that has the machine depending on where you live. It's all that I will use on my 2005 S Type R. It does make a difference. I am still not convinced about Nitrogen but it certainly can't hurt!!!
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I agree that it could be your tires are not round. I had a similar problem on a previous car ('86 Olds 442). The car would vibrate at various speeds and the tires were balanced many times both on and off the car. I had two sets in a row do that and nothing I did stopped it. Finalyyyy, the second set wore out and I had a different brand installed, balanced and aligned. WHAT A DIFFERENCE. Smooooooth at 100 + mph on the fwy.
Square tires do happen...