Yes they do make chatter type noises all the time really but they should be fairly low level compaired to say may cockatiel who will scream out loud alot.
Maybe they are still adjusting to the move to your house and the missunderstanding of where their other older owner has gone. They are surprising clever and so might just be distressed.
Do you know what the previous owner did with the birds or can you ask someone who knew how the birds were looked after. Maybe the previous owner did certain things like letting them out to stretch their wings and fly around, or maybe played music to them???? If they are not getting the same routine it might be upsetting them.
Is there cage in a good location i.e. not too cold/hot, busy/isolated or loud. They do like company even thought they have each other. If they get to loud you can put a clover over them, if you make the cage dark you go quiet. But be careful to put the sheet on carefully because it make unset them more, being in a new home and all.