I have a 99 Cherokee as well...experieced the same thing. Around 75K, I replaced the power steering pump and the noise got better, about a month later the noise was back. It turned out to be a bad water pump. I replaced it and it sounded like new. The water pump and power steering both went bad about a month apart. The water pump almost sounded like a bad valve...a chattering noise. It was most noticable right before shifting to second gear. When you accelerate through first gear and then let off and it shifts to second. Right when RPM's were higher, but not a lot of load on the engine. But my tensioner pully is still working fine. Hope this helps