it is a resonated exhaust tip. thats it.
here is a good exhaust:
IXIL Oval Xtrem Inox Full System YAMAHA XJ6 2009 on | Motorcycle Exhausts | Performance Parts
it is 740.63 total cost shipped from uk to usa and it actually sound/looks good.
here a video:
Ixil Oval Extreme en Yamaha Xj6...