Hello! Thanks for your question.
Among other benefits, concealed cisterns are traditionally much quieter than conventional cisterns - mainly due to the fact that the cistern itself is insulated within plaster and tile.
It can depend on other factors as well though, such as the material and quality of toilet & cistern you purchase, as well as the quality of your pipes/plumbing within the home.
We would always recommend installing a reputable good quality brand such as Giberit to minimise any concerns or issues.
Best choice: use of timber or aluminium for large doors
Noise Levels of Outdoor Aircon Units
Second Storey Flooring Options
Double or triple gazing for windows to keep out the traffic noise