I've got an S-type 2.7D sport at the moment, and I stuck to the Pirelli Zero's that it came with as the ride was good, the handling and grip were fabulous (well not so good in winter, but that's to be expected with these tyres), and it was reasonably quiet (quieter than my previous car - Citroen C5 with michelins).

I had a test drive in a new XF some time ago and it was really quiet, but the car I am thinking of buying (2 year old, new set of some strange make of tyre fitted by the dealer) is not really quieter than my S-type.

Is this likely to be the tyres? Should I persuade the dealer to fit something reputable?

 

Yes and yes. Good tires are expensive for good reasons in addition to the "coke" effect (advertizing adds to the cost of products heavily promoted). Those no name tires are probably to blame. Try driving it with open windows and see if you can identify the noise. Tire noise is distinctive.

I once ditched a perfectly good set of Toyo snow tires because they were very noisy and rode like wooden wheels. Great winter tires...for a pick up truck.

Pirelli make some of the quietest and best riding tires with equivalent performance to relatively noisy Bridgestones or Michelins. Bridgestone and Michelin sacrifice a bit of ride comfort and a bit of noise for slightly better grip and handling, especially dry handling.

Continentals and Goodyears are also relatively quiet and soft riding for equivalent performance. "Equivalent" is not the same as equal, there is no free lunch in the tire business.

 

Tires can make a huge difference in ride, handling and noise. It is hard to generalize as to such qualities just by brand alone. There are also significant differences in characterisics among models within a brand, and even among sizes within the same model.

Having owned performance cars (sedans, coupes, you name it) for quite some time, I've gone through many sets of tires. The tradeoffs are different for each mfr and model, depending on their philosophies and technologies. Some super grippy tires are very noisy, but others that grip as well or nearly so might not be, and at the same time trade off some other quality such as having less wet traction.

Some comparison testing is often helpful. Check out some of the latest max performance tires as an example. Clash of the Titans: Testing Two New Max Performance Summer Heavy Hitters

 

and fittted a set of pirelli P0, so all is well, really enjoying this car