Hi, everyone, bit of a newbie here. bought an zxr250 2 weeks ago. fair condition, test ride didnt indicate anything funny, but as of 2 days ago i have a bit of a problem. When i start the bike (as well as a 15 year old import starts..) its starts well. The issue is that on acceleration up to about 4000 rpm there is a slight, clinking rattling noise, which dissapates from 4 - 8000 rpm then starts around 9 - 100000rpm. When i ride and keep the revs about 8000 rpm the bike sounds fine, but when i pull in the clutch lever and change down there is that sound again. When i come to a stop and put it in neutral there seems to be a slight, non-obviously but definately there ker-plumking kinky thing thats happening. I hope this is not a stupid comment but it sort of sounds like the valves or pistons are knocking about with lack of lubrication. But im not sure where to check the oil, so i dont know what to do from this point other than take the bike in for a service. any help or info appreciated.