https://www.amazon.com/dp/B01CTM0H1S...v_ov_lig_dp_it
Easy to build, easy to buy.
The noise doesn't bother us so I haven't done this yet.
When I put in the thermostatically controlled duct to the basement, I'll put these in while it's all torn apart.
(I think a 2 liter soda bottle stuffed/lined with scotchbrite would work really well.)
(so would a plastic shoe box from Walmart with some cardboard baffles duct taped inside)