Easy solution… stop coasting 
Yeah, you can tweak the sound a bit with more or thicker lube (accepting some risk mentioned).
There are a range of different freehub mechanisms with associated sound from crazy loud to silent. If you really have a preference, it’s possible to dig in and find the more quite versions and either get a wheel with them stock or consider a custom build as needed. Lots of cost and hassle in the grand scheme, so it would likely need to be a big issue to justify the effort, but it’s possible.