This weekend my wife was driving our 04 Subaru outback, while passing a slow moving car, the motor made an odd shutter tap noise while hitting the passing gear. It had a bit of an intermittent shutter noise the remaing 5 miles to town. When we pulled into a gas station the oil light was flickering on and off. After letting it sit, I found it was low on oil (not registering on the dip stick) I added a quart and headed back hom. after that the noise became a light clunk at idle. The clunck disappeared off idle until 2500 rpm. I never lost any performance whatsoever on the drive home, and from the drivers seat of the car you would never know there was a problem. It appears the car as about 2 1/2 quarts low when the problem occured. I checked the timing belt tesioner, everything looked fine (just did timing set and head gaskets 20k ago) I pulled the oil pan today, and there is alot of metal in there. A couple pieces of what appears to be aluminum the size and thickness of finger nail clippings. And alot of smaller to medium size shavings as well, all are non ferous and appear to be aluminum. I checked the rod bearings while in the oil pan and everything appears tight. From what I could see of the wrist pins and piston skirts, everything looked good. I'm not really sure where to go with this project.... I was pretty sure the knock was coming from the front of the motor, but my old man thought it was coming from the back (we both have terrible hearing) it seemed to me to be slighly louder on the drivers side.Any ideas as to where this knock could be coming from would be greatly appreciated.