I took both my rear wheels off to paint them and thought i would check my brakes. Found a broken spring and noticed one cylinder leaking (i probably caused the leak when struggling with new return spring). I replaced the cylinders and springs on both rear brakes (shoes still had 4-5mm of meat).
Used a turkey baster to suck old fluid from master cylinder before bleeding/flushing lines with new fluid.
I now hear a chirping/squeaking noise from the front of the vehicle, whenever I press the brake pedal down (maybe at master cylinder?). This is with the truck not even moving since the paint is still wet on the wheels so i haven't mounted them yet.
I did a google search and found some cases of similar issues that were cured with brake fluid flush. Could it also be caused by a brake fluid flush? Or did i just do a lousy job of bleeding my rear brakes?

Would really appreciate input from anyone with experience or knowledge about this.

Thanks, John