We moved in a new house 3 years ago and have a very unpleasant odor coming from
The heat vents when we run the heat. I reviewed answers to similar questions and found one that may be the problem. The answer suggested there maybe mold in the heat ducts
Or A coil or stagnant water at the A coil drainage. Are theses problems correctable by the average homeowner or do they require a professional?
Thanks!

If you have a way of cleaning the duct have at it. If you can gain access to the A coil you can clean it also. If you do a search here you will find all of this covered before as to what cleaning agent to use etc.