i checked out this 1990 4runner V6 this evening and it had this strange wheezing noise- same noise you would hear when you squeeze a baseketball with a tiny air leak or something. Anyway, its directly related to the brake pedal it seams. when i pumped the pedal and held my foot against it- i would hear this little whistle, i could stop it by applying more pressure. any idea on what this could be? it seemed somewhat intermittent as well.

 

how are your break pads? there is a little wear indicator that makes noise at first, but will not make noise under more pressure

 

the noise sounds like it could be coming from inside-are you talking about something like a little audible buzzer indicating brake wear?

 

Some more info needed, when does it make the noise, engine running or off, when driving or sitting.
Could be a slight vacuum leak on the brake booster. You would hear this when the truck isn't moving.
What jimabena is referring to are small metal ears on the brake pads that touch the rotors when the pads are getting worn, they make a high pitched squealing noise when you stop.

 

definately sounds like an air leak somewhere inside the cab. vehicle was parked- cant remember if it was running or not- probably running and it made this noise with the e-brake on and with it off as well