Rusting burner inlets

On my second heating season with an Amana AMEC960803BN. After the 1st season I noticed some rust on the upper part of the burner inlets to the heat exchanger tubes. Not bad but I pointed it out to the tech during this years fall service. All he suggested was that they do that sometimes. Didn't feel real confident with that answer. Anyway I checked it again last week and the rust is worse. The intake air is taken from the basement, it's about 2400 sqft and open so no pipe to the outside. I noticed that when a heating cycle ends, I can feel warm moist air rising out of the intake opening. Has to be coming from the heat exchanger tubes so whatever moisture is left in there after shutdown is evaporating out and causing the rust.

I'm searching for a better tech but wondering what your thoughts might be on the cause and/or best fix if any.

Thanks

source https://hvac-talk.com/vbb/showthread.php?2225638-Rusting-burner-inlets&goto=newpost