when my riding my pro up the road in the higher gears there appears to be like an on and off knocking at gentle revs or i cnt quite explain it at first i thort it mite be the disk guard or something but it sounds too close to the engine .any one got any ideas or am i jus over acting and also how long shud it take for the fan to kick in mine comes in after about 5 10 mins ive checked the coolant level its full, again any ideas?????????????Thanks for anyfeedback in advance much appreciated