Front transmission pump is hydraulic but when they fail or starve for fluid they often sound like the grinding PS pump. It's time to use extreme care and a very trusted helper, get a tech stethoscope and pinpoint it if possible.
Its hard to hear exactly where from but could it be a heat shield vibrating. I'm new to Lexus but not failed automatics, I have never heard one make that sort of sound before. I have heard torque converters make some strange sounds but this one is new to me.
Motor/trans mounts allowing the engine to twist and touch something under load? Is the video in drive or park/neutral?