OK TT'ers, before you jump on my back...I spent the last two hours search this for help and I recieved a lot of information but nothing really touch my problem. 98 yz400, seems to be making a rattle type noise (not knocking or clunking), like something is coming loose. But where my problem differs is that it only makes it when the bike is warm or hot. Unusally 20 minutes into a good constant pace. NO real power lost, but I didnt pin it either when I heard the noise. Shut the bike down and gave it a look over, because of clutch work done recently (checking for leaks). When I fired it back up the noise was gone and everything ran fine while I took it back to the truck. This is the second time I heard the noise and both times were at least 20 minutes into the ride, but once shut off...it goes away. So this is far from a constant noise? Any ideas?