Floyd,
I don't own an HT-44 but looking at the manual, it uses AALC like some other Hallicrafters gear.? Possibly part of what you're experiencing is a low-threshold AALC.? Temporarily disabling it may help in localizing the noise source. From the manual:
"An outstanding feature of the HT-44 is the amplified Automatic Audio Level Control (AALC). The AALC circuitry virtually eliminates splatter commonly caused by excessive audio gain and its?
resultant 'flat-topping."" This is accomplished by providing up to 12 DB of compression..."
Paul, W9AC
Paul Christensen