Our two 16K units are self-contained, without individual sound shield. Each is mounted within the space it's intended to service (one for the saloon/dining/galley area, one for the staterooms/head and with an extension to the galley). The saloon unit is behind a bulkhead behind a couch. The lower unit is underneath the master berth.
There are two noise components, one being the compressor, the other being the air handler. Both are acceptable for us, but I understand the newer units (e.g., Vector Turbo) are more efficient, and quieter even without the sound shield.
I would guess the optional sound shield would dampen (or contain?) compressor noise... but it may also slightly complicate access for service.
We run the fans approx. 24/7 and I notice that noise more than the compressors, (which only come on depending on demand). OTOH, we also run three more counter-top fans approx. 24/7 too... so we've got lots of fan noise almost all the time.
Our units are in serviceable locations. Not sure I could identify a useful alternate location for compressors in a split system...
South River, Chesapeake Bay