99 Grand Vitara make very intermittent noise

[Sebasten]

I have a 99 Grand Vitara (5 spd., 105 k miles), that has started making a very intermittent noise that lasts about a second or so. The noise sounds like a flute,
penny whistle, or a short tap on a car horn (without dissonance). It can either be a single tone, or move up the musical scale. It seems to come from the area of the gearshift or transmission. Typically it occurs when engine is at idle.The noise seems to be getting more common, but still may only be a few times a day - too seldom for a mechanic to be able to listen for it. Any suggestions as to cause and/or remedy?Puzzled