Thank you for the suggestion, M60A3Driver, but we've been through the common causes such as the one you suggest, to no avail. The noise is deeper than a whistle and varies with temperature, gear and speed, so sounds like a flute or oboe or clarinet or saxophone - take your pick! - until it disappears when the engine is warm. I think it must be to do with the mechanics but can't figure out what. The car has only done 62,000 miles, by the way, and drives normally apart from this mysterious noise. I suspect it is related to the recent replacement of prop shaft bearings but mechanic says no. Any other ideas?