alright when i am dirving sometimes my car will act like there is a vacuum leak and start HISSING really loudly..and the exhuast gets almost silent..and the car acts like the fuel injectors are clogged..i heard somewhere that this could be a bad catyletic converter...is this true..any help would be aprreciated..oh and it has the 2.8 mpfi and yes i checked its not a vacuum leak or a the injectors

dustin