Help a newbie out...I recently bought a 2000 Subaru with 50K miles on it, and the previous owner had done all oil changes himself about every 4,000 miles. I just changed the oil for the first time after running about 4500 miles on the last oil (Shell 5w30 + Purolator filter). After I poured the (very black) oil out of the drain pan, I noticed on the bottom dozens of small metallic particles, maybe the size of a grain of sand or a little smaller. This being my first ever DIY oil change, I have nothing to compare it to, but my common sense sounded an alarm. Is this really bad? If so, what could be the problem? I just had the car looked over by the dealer when they did a tuneup, trans and differential service and fuel filter, and they said everything seemed great. I'm just a little concerned, although I am still under warranty.