My new heating & air system was installed in Fall 2008, but they did not hook up the heat pump. In Fall 2009, I had the heat pump hooked up and then a chalky, musty odor started coming from my vents. I have had 4 different people look at the problem, had my ducts cleaned and have a deodorizer inside my heating unit; however, nothing has helped. I can't stand the smell and think it my also be the cause of my continual sinus infections (not sure, but a hunch). It seems to be all over the house and it even smells when just the fan is running. Any ideas or help are greatly appreciated!

What type of air filters are you using on your system? Are they the cheap ones or the expensive ones?

They are pleated Air Filters I purchased at Ace Hardware. Not expensive ones I am assuming.

What you might try at least a few times are the ones marked "ultra allergen" and they are fairly expensive. They can cost between $15 and $18 dollars.

They may help with your problem. Most air is recirculated in a system (closed) and a filter can make a big difference.