07 xc70 128k, out of storage(outdoors) after 14mos. No brake issues before storing. Depress brake pedal, start car and when i release brake pedal there is a loud whine/gurgle/vibrating sound. No sound when i apply brake, only when I let up the pedal. I keep pumping the brakes but it keeps happening. Goes away after 10min. or so of city driving, but happens again whenever I restart the car during the day. Brakes work just fine. No codes. Noise is too loud under the hood to pin point it's location other than its' the driver's side. Wiring and hose to brake booster show no visual damage but I suspect the booster could be involved. Any thoughts?

 

Might be coming from the oring between the master cyl and booster (#2) - spray something on it and see if the noise changes. (with the engine running) Brake cleaner if you don't want a mess to clean up, or something like wd40 if you don't mind cleaning it up later (when you are replacing the oring)

 

Thanks. I'll work on it this weekend.