Ok, today a 2000 YZ426 came on my local craigslist for cheap so I went to check it out. It was making alot of noise that it wasn't supposed to. I know this because I just sold my perfectly running 2000 YZ426 about 3 days earlier, and it didnt make noises like these. I know that they have a few issues since they were the first year design but I'd like to know more about exactly what the issues are. I've read thread after thread and don't quite understand it all. I read that having aluminum skid plate on the bottom made the noise quite a bit louder, so I took this off and it made it about 1/2 as loud so I could diagnose the noisy area a little better. It runs strong, has no issues starting or running or even idling, but it makes alot of noise. The noise seems to be coming from the bottom of the engine, noise on both sides, but if I had to pick one I think the noise would be louder on the clutch side. I havent been able to figure out what exactly the weak link on the 2000's is in there and what I need to look for when I pull off the cover. I also am going to check the water pump , because I've read about those as well. It shifts through all gears, rev's high and grunts low but the noise is killing me. The guy I bought it from said that he's been riding it like this for the 5 years that he's owned it without any problems, but I just can't handle it. any diagrams pointing the the weak part(s) would be AWESOME! or any other ideas would be alot of help. Also, I think that the noise becomes louder when the bike is at an idle than when it is moving, hot/cold engine doesn't change the noise. Thanks for any help!