Re: dripping sound in heat runs
The noise is probably either the natural "tick" of heat expansion and contraction of the ducting, and/or where rigid sections of that duct pass over/through framing and come into contact with it, rubbing as the duct expands/contracts. The former, there's little that can be done, the latter would be to find the places where the duct is rubbing on things and isolate it with insulation or separation.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!