2001 Lx 470 Humming Noise

[gdona]

I am hearing this humming sound when i am fully stop and the car is in drive. I noticed it makes this sound at around 800 rpm, if the rpm goes up to around 900 the humming stops. The engine runs smooth even when the rpm goes down to 800. I am thinking that this could just be a normal thing. Any suggestions will be great!

[lexus ls430]

i would take it to the dealer