We have a high efficiency furnace in our attic (new construction). We hear dripping noise in an interior wall. There is no noise in the attic. Is this condensation?

You need to trace it out,, look for the source,, before some high dollar damage is done, is possible a condensation pipe stopped up

Oh believe me I am trying. I am currently sleeping alone if you know what I mean. This noise sounds like water dripping from heat ductwork between the walls. From the attic I can see the 3 heat and 1 return in this wall. There is nothing else. It seems to happen mostly at night. Our humidity in the house is only 30%.?

High efficiency furnaces make water they are supposed to, the water has to drain out ,either into a pump that sends it outside into a drain gutter or somewhere, if the drain is stopped up or pump not working this means trouble