A whining sound from the rear of your Jaguar XKR that changes with load often points to the rear differential, as worn gears or low fluid can create that “waa, waa” pitch, but wheel hub bearings are also a strong possibility since they can produce a rhythmic growl or hum that gets louder when coasting or shifting side-to-side. A quick way to differentiate is to check for play or roughness in the wheel bearings by jacking up the rear and spinning the wheels by hand, while also listening for Agricultural bearing noise with a mechanic’s stethoscope; if the bearings feel smooth, then the differential bearings or gear mesh are likely culprits, and checking fluid condition or metal shavings in the diff oil would be the next step.