problem with the svo

well i drove down to tristate raceway last saterday but it got rained out so no one was able to run, but anyway on my way back home i was cruising down the interstate when out of no where my exhaust note changed, it went from not hearing the car run at all to hearing a deep growl while cruising on the interstate. My dad and uncle thought maybe my turbo seized so i gave it a little gas and it spooled right up to 15 psi like normal but the turbo sounded louder then normal and it didnt pull hardly at all. Also since ive bought the car ive heard a vibration while accelerating that sounds like a loose baffle in a muffler just its not coming from the mufflers it sounds like its coming from under my feet where the cat is, and the vibration isnt there anymore. also on my return trip home i lost 3 mpg and i babied it home so i should have gotten better. I was thinking the cat clogged but i dunno if one would just clog suddenly like that. Sorry for making this so long, and thanks for any help.

i want to keep the car as original as possible, i have my run of the mill notch to modify the crap out of and everything underneath the car still looks darn near new the exhaust dont have a touch of rust on it except the pipe that runs off the back of the turbo.

well today i climbed under there and cut out the cat and took it for a drive and wow, theres a huge difference in power now, ussually on a good day if i take off from a start i can only chirp second after spinning through first, now it spins through first and second and gets a lil chirp off third, tommorow morning its getting the pipe installed where the cat was.