Hi Barbara Ann.....welcome to the Club
It sounds like the hydraulic lifters are starved of oil on start up.
If the oil cannot fill them instantly or they are draining down easily then I would change the oil to a lighter weight grade and see how you get on with this.
Also have the oil filter changed at the same time for a genuine Lexus part.
Ensure the oil is as good as you can get (e.g. Mobil1, Castrol, etc)