Ah- this happened to my on my 1991 Lexus LS400 and it went fast! Around 219K, I was setting in a drive-thru one night and all of a sudden it sounded like my engine was knocking! I pulled over and noticed that the pulley was wobbling. I thought it was the water pump, but later discovered that the fan runs on that bearing.

I drove the car home very slowly, sounding like it was going to fly apart any moment. I made it home, but was not wanting to attempt to drive it to the mechanics, so I had it trailered to the mechanic and had him put on a new one. Water pump and timing belt had only 23K on them, so we didnt replace those. $125 labor and $160 part, I was back on the road.