The simplest way to sex your bird is this,how easy depends on the color mutation.
Up to 6-8 months both male and female carry these markings , under their wings ,if you hold your bird up to the light ,on the flight feathers you will see what appears to be yellow spots, these are more prominent in the dark or normal colors, they will also have bars on their tails.
The male looses these features when moulting only the female retains them.
These spots can be seen on Lutino's as they appear darker to the color as for the squeaky noises this is of enjoyment.