I have a 2002 blazer 4x4,that has a hissing noise under the dash drivers side,it goes away if i step lighty on the gas,as soon as i let off it comes back,and it is very annoying,any ideas what it is.
Thanks Al

 

you have a cat stuck under your hood.

j/k, prolly a vacuum leak.

 

I thought that,maybe the brake booster,is there a valve for vacum pressure i can check,and where might it be located.