1995 VW Jetta GL 2.0l 4Cyl

check engine light came on and there is now a rattling noise coming from what i think is the cat converter. if it is the catalac conv. would the check enginge light come on? the sound only happens when i press on the gas but quits if the rpms start to rise. its also starts to bog out like its gonna die if i try to rev it. could this all be because of the catalac conv? at 70 and hour plus material what am i looking at for cost.