So two weeks ago i changed rear brake pads to my 2004 Corolla and when job was done and i was pumping the pedal i noticed that pedal started to hiss. Brake job was normal to me. Old pads were so thin that the piston inside of the caliper was pushed out. So i had to push it back with C-clamp. Before doing that i opened the cap of brake fluid reservoir. Piston went in and i changed pads. Did same to the other side. When job was done the brake fluid was over the max level at the reservoir, so i took some fluid out with syringe. Then i closed the cap and went to pump pedal and it was hissing. Any suggestions what happened? Other than that the brakes and pedal works normally (did some brake booster tests with the pedal) and there isn't any fluid leaks. So im pretty confused here. And I took my car to local Toyota dealer/mechanic and they said that this sound is normal. How can it be normal if it didn't occur before? I'm reluctant to accept that. Before this pad job, the pedal was silent. I remember this well, because few months ago i changed font pads and i did everything same way as this time and pedal didn't make any extra noises then.