90 4runner auto v6 160k . I just got it,and there is an annoying sound which kicks in when you press the brakes while driving and upon releasing the brake pedal or when running slow (15 miles/hr speed). I can hear it from the driver's side engine bay right where the airbox-air intake is located. btw, there is a drop in K&N in the air box.
help! before i damage my eardrums.

 

heres a long shot, but try pressing the brakes and releasing as you are rolling down a hill with the engine off (on a private, non traversed road of course)... or is it definately NOT a brake issue?

 

not a brake for sure.

 

vaccum leak ?

 

probably but why during deccelaration, and which part to check...

 

If you are shooting down all of the suggestions without checking them then how are we supposed to help you? Im not trying to be a jerk.

 

Something with the brake booster possibly? I know on my 94 the booster is bolted right to the firewall where you are describing where the noise is.

 

yes. i just checked all the vacuum lines accessible but the sound is still there. I just cant check the engine while running...