once, spotted the problem on a Saab 9-7X model, precisely – Saab reports that some 2005-08 Saab 9-7X models may produce an irritating squeaking sound when the brake pedal is slowly applied and released.
One possible cause for the noise is contaminated brake fluid, which tends to swell the seals in the master cylinder. To make a definitive diagnosis, have a buddy apply and release the brake pedal while you pop your head under the hood.
If you can isolate the squeaking noise to the master cylinder area, you’ve nailed the contaminated fluid as the cause of the irritation.
Draining the master cylinder and flushing the brake system with a new DOT 3 brake fluid (Part No. 88862806) should silence the noisy pedal.