Trane 2.5t variable speed electric air handler with 10KW auxiliary And outside heat pump Install replacement 20x20x1 pleated air filter, test run all equipment in heat pump mode, test run all equipment in emergency heat mode from the thermostat. Confirm 10KW operation, Upstairs return air grills are humming most likely due to restricted or undersized ductwork but otherwise the system is running in good condition considering the age