Start with what flat noise really is
Bird noise in a flat is rarely about a bird being badly behaved. It is usually contact calling, excitement at predictable triggers such as the vacuum cleaner or a doorbell, boredom calling from an empty room, or the natural dawn and dusk vocalising most parrots and many smaller birds do. Thin floors, shared walls and hard modern surfaces then carry that sound further than it would travel in a house. Reducing what neighbours hear therefore has three levers and you need all of them: where the sound starts in the room, what the room does to it, and why the bird is making it at that moment. Tackle only volume and you will chase the problem; tackle the cause and the volume usually follows.
Placement and the room itself
Sound reflects off hard, parallel surfaces and amplifies in corners, so the worst spot for a cage in a flat is a bare corner on a shared wall. Move the cage to an internal wall that is not shared with a neighbour's bedroom if your layout allows it, and put mass and softness behind and beneath it: a filled bookcase against the wall, curtains rather than blinds, a rug under the stand. Even hanging a thick throw or tapestry behind the cage takes the harsh edge off calls that would otherwise bounce straight through. Keep the cage away from the hallway wall if neighbours pass on the other side, since birds often call in response to footsteps and voices they can hear but not see.
Routine: predictable birds are quieter birds
Birds call most persistently when the day is unpredictable. A bird that never knows when its person will appear keeps checking, loudly. Fix the anchors: wake and uncover at the same time, first social time and first food soon after, a substantial out-of-cage or play session at a regular point, and a clear wind-down into a covered, dark sleep period of proper length at a consistent time each night. Meet the need before the calling starts wherever you can; a bird whose flock time is guaranteed spends far less effort demanding it. Keep departures and arrivals low-key, since dramatic greetings and long apologetic goodbyes both teach the bird that comings and goings are the main event of the day.
Occupation during the loud windows
Most flat owners know their bird's loud windows: early morning, the return-home hour, and any moment of household excitement. Put effort exactly there. A foraging breakfast that takes twenty minutes of shredding and searching competes with the morning chorus in a way a full bowl never will. A shower perch session, a training game of a few minutes or a new cardboard box to dismantle can carry the bird through the evening peak with its beak busy. Teach a quieter contact call by answering soft calls promptly and warmly while letting loud ones pass without a response, then engaging once the bird offers a softer sound; over weeks the bird learns which voice brings its flock running.
Neighbours and the longer view
Introduce yourself and the bird before there is a complaint, explain the predictable peak times, and ask neighbours to tell you directly if a particular period is a problem, such as a baby's nap or night-shift sleep, so you can weight your routine around it where possible. If noise suddenly changes character or the bird calls almost constantly where it once settled, have it checked by an avian veterinarian, because pain, illness and hormonal surges can all present first as vocal change. Most flat birds, given placement, routine and occupation together, settle to a level neighbours accept as ordinary flat life. Using KinsLe Care Teams to assign the wake-up, forage preparation, play session and cover-down keeps those anchors at the same times each day, which is the foundation the quieter behaviour is built on.