I live on the top floor of a four-story apartment building in DC and have been experiencing a terribly annoying noise all winter long. The noise seems most frequent when it is cold, especially at night, and as best as I can describe it, it makes a "click-click-click" as if a mechanical switch is misfiring. The noise is coming from the top of the closet where our Carrier unit is, but our unit doesn't need to be on to hear the noise. It might be related to defrost mode, since sometimes we hear a "swoosh" sound and end of the "click-click."
Our guy came to look at it and, of course, it wasn't making the noise then. He told us it must be something wrong with the roof part of one of the other units, but wasn't really helpful.
We are nearing the point of insanity with this noise as we try to sleep. Can anyone help??? Thanks much in advance.