Low brake fluid and squeaking brakes are two separate issues. When you have a low amount of brake fluid, it can cause problems for your brakes, but it will not lead to squealing in most cases. When the squealing on your brakes occurs, it could be for several reasons. The brake pads could have dust or grease on them. The brake pads also might be bad and the rotors are going bad as well. Simply adding brake fluid to your car will not fix the squeaking. You need to have your brakes checked out so that you can avoid serious problems.