Hell Jay,
..in '81..nice..so we have met "the lady furnace" about the same time ..don't take it too personal..but, it is a very touchy subject, to say that those two pieces of 26 gauge metal , with a strip of fabric in between, installed on the top of the furnace, which weighs about 180-200 lb's, (if with a/c coil more than that) can produce "serious vibration sound" which is to be heard on the other side of the system, through the return duct..today, most, or better to say, all of the residential furnaces are equiped with direct drive blower motor and, if sized properly (static pressure requirement), should not move to make vibrations while operating ..because of what, many municipalities do not require anti vibration damper to be installed.. if that furnace, as described, is able to move and make duct's on its top, which are 6-7 feet above ground, produce "serious vibration noise, there must be some serious installation issue..
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Furnace connections are made up of two basic sections. The gas burner, AC and air handler are on the bottom, and immediately above is the main supply duct which services the house with hot and cold air.
Those two sections are separated by what is called a vibration damper. It is made up of two pieces which attach to the ducts and are separated by a rubber membrane.
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..and, here, you have described "furnace connection", but, aren't the furnace connections known just as "supply" and "return" connections which are determined by the rotation of the blower known as airflow..everything in between is a furnace itself..no need to cut the furnace into a pieces.. the house air distributing system is not a "furnace connection"..
..forgive my ignorance, but proper terms are very important..especially if we are to be hired to judge someone elses work..
