Do not blow hard
Do not blow the saxophone hard. The problem of the saxophone continuously squeaking may also be because of too much air in it. This may also affect the sound of your instrument. Try to put your focus on the air stream to determine how hard you can blow the instrument.
Adjust the reed
Reed in the saxophone is responsible to produce the sound. So, if t he reed is not in the perfect position or shape, you may definitely have problems with your instrument. Check the strength of the reed. If the strength is hard, it definitely will be very hard to blow also. So, change the reed strength as the harder you blow, the more air will be used. This will cause the saxophone to squeak.
Try another reed brand
If the problem remains even after changing the strength of the reed, change the reed brand that you use. You can replace the reed brand with a brand that is renowned in the market or a brand that is preferred by musicians.
Check the mouthpiece
Open chamber mouthpieces are the best as they control the amount of air inside the saxophone. If you do not have an open chamber mouthpiece, get a new one.
Thoroughly check the horn
This is the last thing you would need and probably the only solution if nothing of the above has worked. You need to thoroughly check whether the horn has a leak or not as that may be causing a squeaking sound.