Best Discription I Can Give Is Whistle
by Robert M
This is a Lennox brand central air and heating unit installed in the attic. It has a metal strip you remove to install the ac filter, and slide into place.
When you install the filter and replace the metal
strip you get the noise at the cold air return in the living room ceiling. If I remove the strip the noise quits.
I tried adjusting the filter, but it is so difficult to work with because of it's design I can do much adjusting.