OK let me try and catch up with you here:
You have '97 wheels/tires, we'll call them W1.
You have '98 wheels/tires, we'll call them W2.
1. Your '98 had vibration problems, you put W1 on and the problem was solved.
2. Your '97 had no vibration problems, you put W2 on and the vibration appeared.
So one or more of the W2 wheels/tires are bad.
There is where I'm fuzzy...the vibration stopped when you put the W1 rears on the '97 or it didn't?
