Hi guys, first post I have this unusual noise i believe coming from my engine. It seems to be happening almost only in 4th travelling around 55-60kmph. It seems to disappear below and above that speed at lower and higher revs. It sounds like a whirring vibration noise, almost exactly like if you repeated "who,who,who,who" with a high pitched voice at about 1-2hz. I have a new chain fitted properly by mechanics and old but still serviceable sprockets. Please help!!!