When i've been riding for more than say 40 minutes or i've been on the freeway, I notice my bike starts to run rough, like the engine isn't revving smoothly and it causes a vibration that your whole body can feel. And when I come to the lights, it has a lumpy idle. Temperature is always only just above cold. Then if I leave it for say an hour, its running perfectly again. This roughness doesn't really effect performance too much but is pretty discomforting. Any ideas on what it might be? it had a major service like 500km's ago.