i have an 06 plate S-Type 2.7TD manual. it has a slight whirring vibration noticeable at motorway speeds which sounds like a wheel bearing. However, every now and again when travelling at 70ish a vibration will start from the rear, and it grows in severity becoming quite loud and violent, a bit like hard braking on very warped discs, or a loose wheel, although it's not coming through the front or the steering. I'm forced to slow down because it's very disconcerting. It'll last a few minutes before dying away. It's happened to me a couple of times, the first time was immediately after an MOT and shortly after I'd just had the rear pads replaced. I had an issue on the way home from the test centre (who hadn't fitted the pads) with the rear n/s brake binding up. Any thoughts?