An extremely noisy disc.

I was leaving the school building after most other students were gone. As I stepped out the front door, I heard a sound like an unmuffled outboard engine to my left (South).I saw nothing, so I stepped down to the sidewalk for a better view. There were no vehicles on the street. The sound was coming toward me rapidly, and then I realized it was above the surface. I was under large trees, so I went to the middle of the street where I could see straight up. A disc of dull metallic color came into view. It was travelling right up the street at approximately 100 MPH. There was a 1000 foot overcast and it was about 200 feet below that. I estimated it to be 40 feet in diameter. I could see no propellor, control surfaces or landing gear. As it was passing overhead, the noise got so loud that I put my hands over my ears, but it did not help at all! I can now compare the noise to an unending stream of fifty-caliber rounds passing close by. At the time, I was fourteen years old and had just started flying lessons.
Date is approximate.  We have met the individual who submitted this report, and we deem him to be an exceptionally credible witness.  He is a former fighter (F-86) and bomber (B-25) pilot, and a former military officer, who has been assigned to the Pentagon.  Our impression is that it would be extremely difficult to find a more reliable, credible, and convincing witness.  This is one of several sightings the same individual has had, and those reports will appear in our database, as well, at a later date.  PD