Thanks for the input so far. I should have been more specific, in that the noise isn't there when the engine is off. By coasting I meant when you take your foor off the gas as you approach a stop sign or traffic light. It sounds like its half way along the exhaust route rather than engine.

Sorry to go on about noises but I have another new one now which is like a rattle, that a child has in a pram, coming from underneath the car (and no I haven't run over any babies without realising!). It rattles for several seconds, regularly, on any surface. Seems like a fairly unique noise that one of you might recognise.

Thanks again.

Tom