just catching up with this second page. hmmmmm. when the switch is tripped, the indoor blower stops running and the compressor continues to run. i am now wondering what exactly is tripping. can you send us a picture of the tripping control * in the case of a tripping hpco switch, it would be just the opposite. maybe this reset switch is some overload device for the blower.
dilkey is right, of course. when you read the static in the duct, you will probably see a problem. as you suggested, if the problem did not always exist, then something has changed.
by the way, you said a 'good' filter creates the suction. that stands to reason, since the lower micron filters have more inherent restriction. the phrase 'pushing serious cfm' could be misleading for us. the sound of air sucking through a filter and a filter sucking into the return could also be an indication that the fan could be running normally, but is being affected by restriction on the entering side. it still sounds like a restriction in the return air plenum area. perhaps some insulation has collapsed or something. also, the information doesn't add up. it only does it in heat mode. the blower is what goes off when this control trips. i'm wondering if we are getting correct representation of the problem and identification of the components. i would really like to see a picture of this reset button and what you are describing as the evaporator fan.