I'm bringing a Hahns Macaw into an apartment. I've done extensive research on sound reduction.
Have a link.
Put the birds in the furthest room from a shared wall, surround the room with as much fluffy, soft furniture. Seems simple, but it reduces sound carrying. If you have the funds, invest in thick cloth wall coverings (
Felt, rugs, or tapestries) or
sound panels.
If you need it, get a fluffy blanket, toss it over the door to their room and close the door with the blanket over it. It creates a sound barrier and closes the room off. It's not 100% but it works.
Other options include
Acrylic Cages which absorb a lot of the sound are actually quite attractive looking.
I imagine that you're cockatiel will not make half the sound of my Hahns when I bring her, but I'm nothing if I'm not prepared.
It really depends on your neighbors! Some in my neighborhood are awful and some are understanding. I've spoken to mine and explained the fact that the bird
will scream twice a day, but I'd do my best to train her not to scream through the day. I've tested out the sound reduction of my apartment by cranking up youtube videos of birds screaming to a very high volume and walking around the apartment, outside, and so on.
Just be sure to really CHECK that before you commit to any building. Newer buildings like mine tend to have better sound reductions, thicker walls, better windows, and so on. Just explain to the person showing the apartment that you have a couple birds, they don't normally scream, but they do make noise.
I don't suspect you'll have a lot of problems with a cockatiel or two, whereas I have to worry. Someone in my neighborhood is rehoming their 5 year old cockatoo due to the noise and I almost had a panic attack.