I have a "package" unit installed (horizontally) in my crawl space. While very little noise can be herd from the air handler I get a compressor hum through some of my floor registers. The compressor is wrapped with a sound blanket. and my duct system runs from a ridgid plenum to a flex duct that connects it to a ridgid trunk line and then to flex duct up to the boots. Most of the noise comes from the boots at the end of the trunk line. The interior of the plenum and trunk line are lined with insulation. Does anyone have an idea of how I can damp down the noise?