Just figured out how to quiet down a WI freewheel.
You know that seal that is facing the wheel, it's cyan. Just drop some lube on that and make a complete seal. And that is it, it is really quite now.... who knew!
You can use just a tiny bit of grease instead for even quieter ride, but it just sounds funny. Very muffled, in a weird way.
Packing the whole ratchet mechanism with grease makes for dead silence too, for like 50km...
On cold days a grease packed ratchet may be so stiff that it will not engage. Also over a period of time the grease may harden keeping the ratchet from engaging. But use in warm weather should be no problem for a long time.