2001 RX300 with 280k km. 1MZ-FE engine. Drained and filled steering reservoir with Mobil 1 ATF. Drained and filled ATF every 20-30km interval Transfer case + rear diff changed Redline 75W90 at 210k km. Sometimes when starting the car after sitting for a long while, there is this almost supercharger type whining noise around 1500rpm and increases with RPM until around 3000rpm where the engine noise drowns it out a bit. However, afterwards, if you start and drive the car all day later, you don't hear the whining noise anymore and it doesn't happen every single day. I traced the noise to be by the airbox and looks to be where the starter is or under it. I can hear the whining noise with a screwdriver placed on the starter. Putting car in R makes the noise louder, but after I turn off the engine and wait a few minutes to turn it back on. The noise is gone. I found this thread with the same sound, which the OP says it's tranny issue and like the OP, I changed ATF regularly, it's never brown or anything and always replaced with Type-IV. One thing I haven't done is take the pan off to clean the magnets and replace the filter(I believe OEM is metal filter). https://www.clublexus.com/forums/rx...
Could it be due to motor/transmission mounts?
If shifting in different gears and all can have an effect on the noise, the powertrain does shift into a different position depending on P/R/D gears?