GPX 250 strange noise

Im new hear, so first i hope im posting this in the correct area. I have a 2006 250R 54,000 on the clock, ive had it for the past 16 months since 12,000km with no probs, used as my primary transport to work, I stopped using it for a week due to weather, yesterday i took it for a ride and noticed a strange swooshing noise that increases as i accelerate and decreases as i slow down. No mater if i have the clutch in or not the sound is still there. Seems to get worse after approx 1 min of riding when its warmed up then the noise stays constant. I initially thought it was the brakes rubbing the discs as i hadnt used the bike for a week, but it should have stopped by now and also the frequency of the swooshing is too slow for brake disc noise, i counted roughly 4 swooshes /second doing 60kms. Ive checked cables and everything that rotates but no luck yet, starting to think it may be the clutch but i dont have any clutch probs as yet and the noise can be heard with or without the clutch in. Hope someone can shine some light on my strange swooshing noise ( its not a knock or a grind, sounds more like the noise you make when you say "sh")
Thanks
Craig
Thanks
Craig