hi, name is brian. i own a 2003 S. about 2 weeks ago i noticed that when i got on the throttle hard in 3rd gear the rpms scream like normal but the car was going no where... then noticed it in higher and lower gears... it almost seems like iv lv lost close to 50% power across the board... and now i started with what sounds like valve train noise... but its not constantly there and its not constantly as loud. if i start the car cold and let it warm up the noise stays. but if i let it warm up, shut it off and start it again its gone...

if it helps at all i tossed a check engine light for o2 censor about 3 weeks ago but it has since gone away.
clutch slipping? supercharger belt sliping? oil pressure? im kinda new to this car so any kinda help would be great before i decide to drop it at the dealer... car has just under 119k miles

thanks!!