My brake started making air sound when I press them when truck is running or off my brakes work fine I am about 99 percent positive it's the filter does anyone know where I can get one and change it? Thanks

 

If your vehicle has a vacuum booster, the air on one side of the diaphram has to go out when the diaphram is pulled by the vacuum. Not something to be concerned with unless the diaphram has a leak.

Not knowing the size of your vehicle , it could have a hydroboost system which makes some noise normally also.