Speak to the previous registered keeper. They might know what it could be, provided they are prepared to admit they sold a car with a problem but at the end of the day its between you and the dealer. He is havering about them vibrating as a matter of course - they don't! If you can pin point the trouble you're halfway there. Just noticed I went on about pads and calipers in my last message, the back end of FLs is drums, have a look inside and check the shoes as well as bearings etc.