Rusting stone chips on bonnet / hood
 

I have had 2 replacement bonnets from Lexus under warranty due to rust bubbling up under the paint. One at 30,000 and one at 90,000.
These are spots of bubbling rust from 0.5 to 1 cm in diameter and look like stone chips have started the process.

This is happening exclusively below the radiator grille, bodyshop says the new bonnets are not galvanised, so am concerned about it reoccurring as the car ages.

Has anyone else experienced this and any advice?

I've just bought a car bra from Lexus of Roseville for shipping to the UK to protect as the Warranty is now expired.

2006 RX400h SE 110,000 miles