finny

A few weeks ago i started to get a "bees in a can" type noise at around 2400-2600rpms. i have a budget y and originally i was assuming that it was a bad flex section. after a few weeks the bees noise faided and i started to get a low pitched rattle. i know its somewhere in the exhaust because rev it hard and the rattle gets louder. visually the exhaust looks fine, i'm assuming the noise is the converter. if this was the flex section is there anyway to visually tell that it has failed?? also from what i read if your converter has failed there is a reason that it has failed. my car is a 99 cali with 85k on it. the cel isnt on, although i do get a knock sensor code when i scan it. other than that the car runs great and i avg about 22-24 mpg city/highway driving. i wish i had a sound clip that would make this much easier, but would this be my cat and why any help is appreciated

jason