Got a noise that sounds like reverse gear (straight cut gears) when driving, I put it into neutral while moving still and at idle can't really hear it over exhaust but revving it still in neutral the sound becomes much louder and only lasts for a short while, by the time I found somewhere to pullover the noise has stopped. Any ideas on what to look for???

 

im no mechanic but could this be cam belt related? tensioner or belt rubbing maybe? Might be worth getting someone to gently rev in neutral, while you try to pin point where the noise is coming from

 

Release bearing? Tension in aux belt?