I would recommend you get to the dealer as soon as possible. Not because anything is potentially dangerous, mind you, but I see this all the time and your symptoms point to a bad catalytic convertor. Big money item, but your cats are covered by and 8 year/80000 mile warranty. The dealer will do the whole repair for free, provided the in service date on the vehicle is less than eight years ago. On a '97 you are just about out of time (I'm hoping mine goes out on my '97 within the next couple of months for the same reason).