My gas furnace is in a dedicated "closet" inside the utility room. The closest cold air return is about 5' away (laterally) in the ceiling of the hallway right by the bedrooms. When the furnace lights you can hear significant combustion noise, and when the fan is blowing the air movement is loud, and fast enough to produce a slight whistling through the vent.
The area around the return vent looks like it's insulated, but the vertical duct (~8' long; it's an updraft furnace) gives a good ring when I thump it, so I think it is not.
Is there anything I can do to quiet the vent? Would replacing the return duct with insulated ducting help? I know a multi-speed blower would help, but this furnace is brand new (new construction). Can I install a more restrictive vent and shift more of the return flow to the upstairs return (which doesn't seem to make any noise)?