Silencer for ducts

[Reno]

I have a small pool in the basement - 8ft x 14ft x 4.5 ft deep. The pool room is isolated from the house with dedicated dehumidifier, heat and air exchange. The problem is that I don't like the amount of noise heard through the floor registers from the dehumidifier and heater fans.

Is there a way to muffle the noise before it reaches the floor registers? Sort of like a muffler on a car exhaust?

[Real Pisser]

Sounds nice; I am envious. I'd live with the noise

[.p.jm.]

Is the duct lined ? Is the noise from the registers coming from the fan per se, or from the registers ? IOW is it low frequency mechanical noise, or air noise ?

[Noon-Air]

yes