Two saucer-shaped objects at low-mid altitude, silver in color, moving eastward in broad daylight over the middle of town.

It was a perfectly clear summer day.  I don't remember the exact date, month or year, but I would estimate the summer of 1987.  I was in my back yard around mid-day and I looked up in the sky and saw two silver disk-shaped UFOs flying eastward toward Lake Michigan at a rapid speed.
We lived in the middle of the city near the corner of South 35th Street and Custer Street.  The objects were flying at about the altitude a single-engine prop plane might fly.  The UFOs were flying at slightly different altitudes but perfectly parallel to each other and at the same speed.
The objects were circular in shape, but not as flat as a saucer.  The bottom of the objects were smooth and metallic, but had seams/crevices originating in the center and extending to the edge of the object, almost like the edge of a scallop shell or sea shell.  The objects made no sound.
The objects were flying directly overhead in an easterly direction.  I ran into the house to notify my mom, who came outside in time to see the objects herself but not in time to capture a photograph as their speed was too high and they had disappeared on the horizon within about 20 seconds' time.
In hindsight, my first thought was that the objects were two round parachutes or balloons, but there were a few problems that would make that impossible.  The objects were flying low enough to tell there was nothing suspended from the bottom-- no person and no scientific instruments.  The objects could not have been parachutes because the bottom of the objects were not concave.  Most importantly, it was clearly visible that the objects were not made of fabric, but of a harder material; and there were no ripples or indentations caused by the wind.  Lastly and most importantly, the objects were moving too fast to be an un-propelled object such as a balloon, parachute, or a fan-propelled parachute.  The object was moving at at least the speed of a small single-engine prop plane-- faster than the wind could naturally move the objects, especially on a clear day.
What is most interesting about this sighting is that it was in the middle of the day, over a metropolitan area of about 35,000 people.
This is the first time I have ever posted this story online, but I have told many friends and relatives about the sighting.  I have done a lot of research to try to find photos of the objects online, similar stories both in Manitowoc and elsewhere, but I have found nothing.   The only similar story is a sighting that took place in 1987 in Sheboygan in the northern sky, also in mid-day.  That sighting is similar in geographic location, time of day, and the color and shape of the object (silver and round).  It differs in that the sighting only mentions one object (not two), and they witnessed oscillation, which I did not.
Witness indicates that the date may be approximate.  PD