Maybe it has to do with the memory settings i.e. seat and steering wheel...i dunno

 

I searched for "2019 Lexus ES 350 start up" and watched few YouTube videos from Fsport and non-Fsport trims, no ones sounded like that, I'll investigate tomorrow. I do have memory seat set on #1 and some custom setting on the odometer and the screen, will play around for few more days to see how consistent I getting this sound.

 

sounds like the memory seats. mine beeps like that when the car is in range of the 2nd set of keys (in the house) and it changes to another memory seat position.

then I have to choose my setting which is on #3

 

If he linked the key with the memory seats, that’s may be it.

 

I think i may have figured it out: it has to do with the memory seats. The car has the tilt back / slide back seats when you turn the car off for easier exit. When you get in and buckle your seat belts, it goes back to the memory 1 setting. IF you start the car before the memory finished setting the seats / finished moving it makes that sound to alert you that the seat hasn't finished moving and is still moving to your desired position.

At least that's what I have seemed to observe. If I let the seat and steering wheel complete their entire cycle/ memory setting before i start the car, I don't seem to get that sound.

 

I don't ever buckle my seatbelt before I start the car but I still get the occasional beep.

 

I have to buckle mine so that the seat starts moving so that I can reach the brake pedal to start the car...