Just took possesion of a newly built house. Ducts were cleaned by the builder. Same company who did the installation of furnace/water heater did the duct cleaning.
After taking possesion, I started looking around. The duct under the kitchen cabinet had not been cleaned. It was full of crap. Gyproc, wood, metal, can of pop, and dust, dust dust. I then checked an air duct where there is a "U" shape connection. Naturally, all the crap was at the bottom of the "U". And there was lots of it. I then checked the cold air return and found part of a salami sandwich.
The builder agreed to have the same folks come back and clean them a second time. They found orange peel, pieces of wood as big as 3" in diameter, coffee cup and more assorted garbage.
The cleaning method is a joke. Connect a huge vacuum on hot air supply and blow air with a gun at entrance of vents. And connect same vacuum on cold air return and insert a hose to blow air in most ducts. No wonder all that crap is left in the duct. Maybe I should have told them I have a "lung issue"...
Another duct they "missed", that was a simple straight line duct to the basement, was full of dust. You could measure the thickness in millimeters.
I was thinking to pay another company to REALLY clean the ducts, but I'm concerned it is a lost cause and might be better off to find a way to do it myself. After I figured out how... Maybe a sort of brush attached to a drill???