I've been a charter pilot in the San Juan Islands for more than 16 years and am used to looking for other aircraft that might affect my flight. I was flying a company Cessna from Eastsound, WA to Bellingham, WA at approximately 9:30am with passengers aboard. Weather was clear. Out ahead of my airplane, I spotted a dark grey, roughly oval object at roughly my altitude of 2000'. It was moving from right to left (south to north) at high speed near Lummi Island. In the timeframe of 5-10 seconds it rapidly became smaller and then disappeared completely. I kept looking for it, thinking it had been an aircraft that had turned away from me, making it harder to see. Then I thought it may have been another aircraft approaching Bellingham for landing. A couple of minutes later, I did hear a Piper Warrior in the pattern at Bellingham, but when I landed and saw the airplane I'd heard, it was red and white, not dark grey like the object I had observed. It remains unidentified and very curious.