ducts and furnaces do not create dust. the only dust in your ducts is what got past your filter into the ductwork and did not get blown out. This is pretty much a steady state situation. yes dust blows out of your ductwork. exactly as much dust as is sucked into your ductwork.
If you have your ductwork cleaned , this will temporarily reduce the amount of dust coming out, but it will rapidly return to the same steady state situation. A better solution is to seal the intake side of your furnace. check the passage and ductwork on the intake side and caulk and tape everything. Change the filter frequently and consider installing a bigger filter to reduce the suction. Duct cleaning is not very effective in contolling dust.