My bike has developed a rapping sound from down below. It's been difficult to pin point the location. It increases with rpm and virtually dissappears at idle. It almost sounds like a spun bearing from days gone by. Performance is unchanged, mpg is unchanged, starts right up but sounds like a bag of chains riding down the street. Oil is good (changed 1000 miles ago). I do get a bit of a hic cup occasionally when at idle. Any help would be greatly appreciated.