I have two Trane high efficiency HVAC's in my home. UH2C100 series. six years old. The one closest to my outside dipole is quiet, no noticeable RFI on 20 meters. The other, which is further away on other side of house, has RFI. Models are identical and installations seem comparable.
I get about an S6 broadband noise when the draft fan on the noisy furnace starts. RFI continues after main blower comes on, but possibly at a bit lower level. Checking with AM radio, RFI is strong in immediate vicinity of top and bottom sections of furnace.
My plumbing and gas lines are PFC so I believe the only grounding to either HVAC is via the AC power back to the service panel.
I installed several clamp-on ferrites on wiring to draft and main blowers. No difference.
Any thoughts on why difference between the two units and what I might do next (other than wait for summer)?