I need some help from you who are far more experienced in 4-strokes than I am. I own an 04 yz450, bought as a left over. It has been ridden 6 times and has about 12-15 hours. It has had the oil changed 4 times and the filter has been changed twice. I am a 44 year old wannabee mxer, but of course like to have fun.... Lately there has been a light rapping/tapping from the engine, kid of in the front, that souonds like a car motor lifter that isn't getting enough oil. It is most noticable when the bike is first started, and lasts for a few minutes and sweems to diminish after a while. I spent the afternoon at a practice track in Maine yesterday, and at first it was very noticable, and at the end of the day it was there but much quieter. The bike is obviously still tight, and starts first kick, and is reliable. The dealer I bought it from keeps saying the bikes are bullet proof, and not to worry,but this doesn't seem normal OR good. It also seems way too early for a Yamaha to have valve issues. Any thoughts? Also, my 2 buddies who own 03 crf's liked my bike more than theirs after spinning a few laps on it.They said it handled better and felt lighter... Yee Hah! Thanks.