I had a grinding/vibrating noise happening only when I had the vehicle in gear and only at around 1200 RPMs. Since it didn't do it in Park or Neutral, and I could emulate the awful sound by power braking (not moving) I immediately assumed Torque Converter-Transmission problem. ATF had good color (Pink not brown), no metal shavings in it, no burning smell. Stall test came out okay. Only heard the sound under a load. Took it in to Certified Transmission in Bellevue for a diagnostics. They called me a couple of hours later telling me the Torque converter and Transmission were fine. A bolt that holds a heat shield near the second catalytic converter broke (rusted out) causing the heat shield to drop just enough so that it only vibrated against the exhaust at a certain RPM under load. I was more than happy to pay for the diagnostic charge and slight fee for them to bolt the plate back up. Honesty and integrity.