I'm a new member and don't know what I'm doing here, but here goes. I joined tonight triying to find something on a similar sound from my RX300. I thought it was the CD changer changing the CD's in and out one-by-one. Tonight I removed the two panels under the dash on the passenger side. One reveals the HVAC blower, the other (a vertical panel on the center console) reveals the coil piping and actuators that open and close the air valves for the different HVAC modes. One of the actuators is making the noise. It acts like it can't figure out what to do - open or close - it just goes back and forth over and over. I would take that panel off and see if it's the same thing. The question I have for someone is: Is the fix to simply replace the actuator or is the problem with the circuitry that controls it?
Hope this helps you.
Tray
