I was changing the oil filter on an 01 Yamaha WR 426. There were about 50 small pieces of iron, since they were attracted by a magnet, in the filter. They were slightly smaller than 0.5mm. Maybe even smaller. Should I tear some of the engine down to see if I can find the problem or is this common? I hear no strange noises and it runs great. Thanks in advance for any help and/or advice.